Use of radioisotopes for rapid identification of microorganisms
This is a division of application Ser. No. 429,629, filed Dec. 28, 1973 now U.S. Pat. No. 3,969,496. 
    
    
     This invention relates to the use of radioisotopes for the rapid identification of microorganisms. More particularly, this invention relates to the identification of an unknown organism by obtaining a radiorespirometric profile of the unknown organism and comparing this radiorespirometric profile to standard radiorespirometric profiles obtained on known organisms to determine to which one it will correspond. By &#34;radiorespirometric&#34; is meant the measurement of metabolism of a microorganism which results in the evolution of radioactive gas from a radioactive substrate. 
     The term &#34;microorganism&#34; as used throughout this application refers to Orders I to X bacteria, mnycoplasma, actinomycetes and fungi which are listed in Bergey&#39;s Manual of Determinative Bacteriology, Seventh Edition, Williams &amp; Wilkins Co., 1957, by Breed, Robert S., E.G.D. Murray and Nathan, R. Smith, the disclosure of which is incorporated herein by reference. 
     The conventional indentification of these microorganisms is a time-consuming and laborious process. Thus, for example, to identify an organism which is present in urine, stools, blood, spinal fluid, etc., the specimen is first streaked on agar plates or processed by other known techniques to obtain isolated colonies of the microorganism. After the unknown organism is isolated, it must then be subjected to a battery of tests to identify it. These tests include colony and cell morphology, stain characteristics, susceptibility to antimetabolites and serological and biochemical properties. Since many of the tests require relatively long incubation times, it frequently requires a minimum of 18 hours after isolation to arrive at a positive identification of the unknown microorganism. A method of microbial identification which would minimize the time required to make the identification would be an obvious advantage in the treatment of a patient since this would permit the attending physician to, e.g., prescribe the correct type and dosage of an antibiotic. 
     Rapid means for the identification of microorganisms would also be valuable in other areas such as to identify microorganisms present in food, drugs, spices, cosmetics, wine, beer, potable water, waste water, air, soil, etc. 
     Accordingly, it is a principal object of this invention to provide a means for the rapid identification of microorganisms. 
     According to the present invention, there is provided a process for the rapid identification of a microorganism which comprises inoculating a number of different  14  C specifically or uniformly labeled substrates, i.e., a substrate which contains at least some carbon atoms having an atomic weight of 14, with an unknown organism. Each of the  14  C labeled substrates is capable of being metabolized to  14  CO 2  by certain specific microorganisms All of the substrates are then incubated for a predetermined length of time sufficient to cause breakdown of at least some of the substrates resulting in the production of  14  CO 2 . 
     Metabolism is defined as fermentative or oxidative metabolism via known and/or unknown pathways, which affects a  14  C atom of the substrate to produce  14  CO 2 . The extent of metabolism of substrates by the microorganism is determined by analyzing radioactivity which is evolved. If no  14  CO 2  is evolved as indicated by the analysis for radioactivity, then it is known that those substrates are not metabolized at the  14  C atom to produce  14  CO 2  by the particular unknown microorganism within the given incubation time. By determining the quantity of  14  CO 2  produced from each  14  C labeled substrate, within a given time interval by the unknown microorganism, there is obtained a substrate radiorespirometric profile which serves as a fingerprint of the unknown microorganism. This radiorespirometric profile is then compared to standard radiorespirometric profiles which have been obtained in the same manner on known microorganisms. By determining which standard radiorespirometric profile the radiorespirometric profile of the unknown mircoorganism corresponds to, one is able to identify the unknown organism. 
     The process described hereinabove for the rapid identification of microorganisms by the use of radioisotopes may be conducted in an apparatus which comprises a means for containing a number of different and separate  14  C labeled substrates, means for inoculating each of the  14  C labeled substrates with an unknown microorganism, means for collecting radioactive gas which is produced as a result of metabolism of the  14  C labeled substrates and means for analyzing any gas obtained for radioactivity to determine whether metabolism occurred in each specific  14  C labeled medium. 
    
    
     The invention will be more fully described by reference to the accompanying drawings wherein: 
     FIG. 1 is a flow diagram showing the process of this invention; 
     FIG. 2 is a perspective view of a microculture tray, partly in section, which may be used in the practice of this invention; 
     FIG. 3 is a sectional view taken along line 3-3 of FIG. 2; 
     FIG. 4 is a view similar to FIG. 3 showing the tray in combination with a cover; 
     FIGS. 5, 6 and 7 are graphs showing the rate and quantity of radioactive CO 2  gas evolved by different microorganisms in the presence of various  14  C labeled substrates; 
     FIGS. 8 and 9 illustrate the range of cumulative evolved radioactive CO 2  gas obtained in a series of repetitions of two different microorganisms on various substrates; 
     FIG. 10 is an exploded perspective view of an incubation unit assembly; 
     FIG. 11 is a side elevation, in section of the assembly of FIG. 10; 
     FIG. 12 is a perspective view of a plurality of the assemblies of FIGS. 10 and 11 stacked for incubation; 
     FIGS. 13 and 14 are perspective views of two forms of collection material carriers; 
     FIG. 15 is a perspective view, partially schematic, of a counting and analysis system usable with the assemblies of FIGS. 10-14; 
     FIG. 16 is a schematic diagram of an analysis and control system usable with the apparatus of FIGS. 10-15; 
     FIG. 17 is a side elevation of a portion of the tray of FIGS. 13 or 14; 
     FIG. 18 is a sectional view of a portion of the tray and guide rail of the apparatus of FIG. 15; and 
     FIG. 19 is a partial plan view, in partial section of the apparatus of FIG. 18. 
    
    
     In accordance with the practice of this invention, standard radiorespirometric profiles are prepared for known microorganisms. Cultures of known microorganisms may be obtained from repositories such as the Center for Disease Control in Atlanta, Ga. (CDC) and American Type Culture Collection. Set forth in Bergey&#39;s Manual of Determinative Bacteriology, Orders I to X, are a number of microorganisms for which standard radiorespirometric profiles may be prepared. In some cases it may be sufficient to merely identify the microorganism by genus. However, in other cases, it may be desirable to identify the particular species of microorganism within the genus. Therefore, in accordance with this invention, it is sufficient that the radiorespirometric profile identify the microorganism as one which falls within a particular group which is differentiated from microorganisms falling within other groups. Species for which experimental data have been obtained include those microorganisms listed in Table 1. 
     TABLE 1 
     escherichia coli 
     Alkalscens-Dispar 
     Shigella dysenteriae 
     Shigella, flexneri 
     Shigelli sonnei 
     Edwardsiella 
     Salmonella Gp B 
     salmonella paratyphi A 
     salmonella choleraesuis 
     Salmonella typhi 
     Salmonella pullorum 
     Salmonella galinarum 
     Arizona (lactose -) 
     Arizona (lactose +) 
     Citrobacter 
     Klebsiella pneumonia 
     Klebsiella ozaenae 
     Klebsiella rhinoschleromatis 
     Enterobacter aerogenes 
     Enterobacter hafnia 
     Enterobacter cloacae 
     Enterobacter liquefaciens 
     Serratia marcescens 
     Proteus vulgaris 
     Proteus mirabilis 
     Proteus morganii 
     Proteus rettgeri 
     Providencia alcalifacens 
     Providencia staurtii 
     Pseudomonas aeruginosa 
     Pectobacterium carotovarum 
     Haemophilus influensae 
     Streptococcus faecalis 
     Each known organism is tested against a sufficient number of  14  C labeled substrates to differentiate it from other microorganisms. The substrate may contain one or more carbon atoms having an atomic weight of 14. Set forth in Table 2 are a number of  14  C labeled substrates which are commercially available and which have been tested. Each of the substrates set forth in Table 2 is assigned a numerical designation or numbering code which is used in FIG. 7. However, the identification method is not meant to be limited to only this list of substrates nor is the position of  14  C carbon atom specified, the only carbon atom which may be labeled and used for the identification method. In this table, the designation &#34;UL&#34; indicates that the substrate is uniformly labeled, i.e., the  14  C label is evenly distributed to all carbon atom positions on the molecule. The numerical designation (s) preceding the names of some substrates indicates the position of the  14  C atom(s). Most of the substrates listed in Table 2 are in the form of the sodium salt, although the free acid form or other forms may also be used. 
     
                       Table 2                                                     
______________________________________                                    
Numbering                                                                 
Code      .sup.14 C Labeled Substrates                                    
______________________________________                                    
 7        UL .sup.14 C urea                                               
10        1 .sup.14 C lactose                                             
18        15 .sup.14 C citrate                                            
19        UL .sup.14 C ornithine                                          
20        UL .sup.14 C maltose                                            
21        UL .sup.14 C sucrose                                            
22        UL .sup.14 C D-glucose                                          
23        1 .sup.14 C DL-lysine                                           
24        1 .sup.14 C dulcitol                                            
25        UL .sup.14 C sorbitol                                           
26        UL .sup.14 C D-xylose                                           
27        UL .sup.14 C D-manitol                                          
28        1 .sup.14 C ring DL-phenylalanine                               
29        UL .sup.14 C glycine                                            
30        UL .sup.14 C D-alanine                                          
31        2 .sup.14 C xanthine                                            
32        UL L-alanine                                                    
33        UL .sup.14 C formate                                            
34        UL .sup.14 C acetate                                            
35        UL .sup.14 C DL-lactate                                         
38        1 .sup.14 C fumarate                                            
39        UL .sup.14 C malate                                             
40        1 .sup.14 C gluconate                                           
41        UL .sup.14 C glutamate                                          
42        UL .sup.14 C L-tyrosine                                         
43        UL .sup.14 C L-threonine                                        
44        UL .sup.14 C L-aspartic                                         
47        1 .sup.14 C succinate                                           
48        (ring 2 .sup.14 C) L-histidine                                  
49        2 .sup.14 C (ring labeled) tryptophan                           
50        1 .sup.14 C DL-leucine                                          
51        1,3 .sup.14 C glycerol                                          
52        1 .sup.14 C D-galactose                                         
53        1 .sup.14 C D-mannose                                           
54        Carbonyl .sup.14 C DL-methionine                                
55        1 .sup.14 C serine                                              
56        1,2 .sup.14 C oxalate                                           
57        1 .sup.14 C DL-valine                                           
58        1 .sup.14 C malonate                                            
59        4 .sup.14 C DL-aspartate                                        
60        (guanido .sup.14 C) DL-arginine                                 
61        UL .sup.14 C trehalose                                          
62        2 .sup.14 C uracil                                              
63        UL .sup.14 C erythritol                                         
64        1,4 .sup.14 C DL-tartrate                                       
65        (carbonyl .sup.14 C) dextran                                    
66        UL .sup.14 C starch                                             
67        UL .sup.14 C cellulose                                          
73        1 .sup.14 C glucose                                             
74        6 .sup.14 C glucose                                             
75        1 .sup.14 C propionate                                          
76        1 .sup.14 C butyric                                             
______________________________________                                    
 
    
     The production of  14  CO 2  from some substrates, such as lactose, is dependent upon the induction of enzymes by that substrate and, therefore, is time dependent. It is preferred to use substrates for which breakdown to produce  14  CO 2  is least time dependent--i.e., substrates which do not require inducible enzymes for breakdown or transport. The rapidness of the test is based upon constitutive enzymes which permit an organism to commence its action immediately. Conventional biochemical techniques utilize substrates which require many hours or days for metabolism. The radioisotopic procedure, therefore, does not conform to conventional results. Substrates which give positive fermentation results classically may be negative by the radiorespirometric method. 
     The media containing  14  C labeled substrates which are inoculated with the microorganisms may be composed of a basal medium containing salts, buffers, growth factors, preservatives and a single  14  C labeled substrate or may comprise simply aqueous solutions of the substrates. These  14  C labeled media may conveniently be contained in a compact, partitioned or welled tray such as a microculture tray as shown in FIGS. 2-5, or in a form separate from the microculture tray which is suitable for addition to the microculture tray. The substrates may be present in the wells of the tray in the form of liquid solutions, gels or in dry form--e.g., freeze dried. The substrate should be present in sufficient amount to provide a readily detectable amount of  14  CO 2  upon metabolism. Preferably, the substrate in each  14  C labeled medium will contain at least four nanocuries of radioactivity. 
     A small amount of suspension of the microorganism is used to inoculate each of the different  14  C labeled media to form a mixture of the  14  C labeled medium and the organism. Inoculation may be performed by introducing the suspension of microorganism manually or by automated or mass replicating techniques. If the  14  C labeled substrate is present in dry form, the aqueous medium used to introduce the microorganism into the means for containing the  14  C labeled substrate reconstitutes the substrate and forms a mixture of the  14  C labeled medium and the organism. 
     Referring more specifically to FIGS. 2-5, there is shown a microculture tray 12 containing a plurality of wells 14. Each well 14 has a round bottom 15. The wells may be dimensioned so as to have a diameter of, for example, one-half inch and a height from top to bottom of one-half inch. Each well contains a medium 16 which includes a different  14  C labeled substrate. After the medium 16 in each well is inoculated with the suspension of microorganism to form a mixture 17 of the medium and the microorganism, the wells are then covered with a means for collecting radioactive CO 2  gas such as with a filter pad cover 18 containing a getter material, e.g., a solution of lithium hydroxide or barium hydroxide. The cover 18 should create a tight seal of the well 14. A separate disc-shaped cover can be used to cover each well or, alternatively, a single sheet can be used to cover all of the wells in the tray 12. All of the inoculated media are then incubated for a predetermined period of time, e.g., from 10 minutes to 4 hours. During this incubation period, if the  14  C labeled substrate contained in each medium is one which is metabolized by the organism,  14  CO 2  will be evolved. This gas is collected by means of the cover 18. Thus, if the cover 18 contains barium hydroxide, the gas which is evolved will react with the barium hydroxide to form Ba 14  CO 3  on the cover 18. 
     The covers 18 are then removed, dried and assayed for radioactivity. The instrument used for assaying for radioactivity can utilize several Geiger tubes which will monitor and record the presence of carbon atoms having an atomic weight of 14 contained on each of the covers 18-- e.g., a Gieger-Muller gas flow counter. The magnitude of radioactivity is measured for each of the getter covers and the results are recorded and used as a standard radiorespirometric profile for that organism. A specific system for accomplishing this is more fully discussed hereinafter. 
     A standard radiorespirometric profile may also be obtained by providing a radiorespirometric profile of an unknown organism in the manner previously described for known organisms. The unknown organism may then be identified by means of conventional biochemical methods for identification of unknown organisms. Thus, once the unknown organism has been positively identified by conventional means, the radiorespirometric profile for that organism may be used as a standard. 
     This invention may be used to identify microorganisms such as those belonging to the genera listed in Bergey&#39;s Manual of Determinative Bacteriology, Orders I-X, including various groups of pathogenic bacteria such as enterics, fastidious gram negative organisms, anaertobes, neisseria, gram positive cocci, Mima Herrilea Group, etc. A radiorespirometric profile is obtained for the unknown organism in the same manner as the standard radiorespirometric profiles are obtained. A pure culture is obtained from a sample of urine, blood, spinal fluid, food, water, air, etc. by streaking the sample material on an agar plate or by other known means. Incubation of these agar plates results in the growth of isolated colonies of organisms. Samples may then be taken from the individual colonies and suspended in an aqueous solution to prepare the inoculum for use in the practice of this invention. 
     The plates or other enrichment media used for obtaining the unknown organism from an isolation specimen frequently contain inhibitors for the growth of all microorganisms except certain species, so that only those species of microorganism which are not inhibited will grow. By the use of such inhibitors of the isolation specimens or in the  4  C labeled media, the isolation specimens may in certain cases be used directly for the inoculation of the  14  C labeled medium. 
     The size of the inoculum, i.e., the number of microorganism cells present in the mixture with the growth medium may vary over a relatively wide range without substantially influencing the results for a given substrate. It is, therefore, unnecessary to make precise and timeconsuming adjustments of inoculum size. In practice, the inoculum used in obtaining the data for FIGS. 5-9 was adjusted to an approximate optical density of 1.0. Moreover, the concentration of the substrate may be varied widely without substantially influencing the evolution of  14  CO 2 . Since large volumes of liquid retain significant quantities of CO 2 , it is desirable to use a minimum amount of total liquid volume in performing each test--e.g., from about 0.05-0.2 ml. 
     The magnitude of response as measured by the amount of  14  CO 2  evolved during the incubation reaction may be expressed in any suitable terms such as counts per minute. The results for a particular microorganism assayed against each substrate may be recorded on a card using lines or holes to indicate the magnitude of radioactive response so that a visual comparision may be made to a similar card prepared on an unknown organism. Alternatively, the data may be stored in the memory bank of a computer and the growth media profile obtained on an unknown organism may be matched by the computer to determine whether it falls within the ranges of response for the various standard radiorespirometric profiles. Statistical goodness of fit could be performed by the computer to give reliability of the identification. Further, they can be recorded simply as positive or negative--e.g, below a certain number of counts per minute, the response will be considered negative, and above that number of counts per minute the response will be considered positive. When the radiorespirometric profile for a given organism is expressed as either positive or negative against a given substrate, it may be necessary to utilize a larger number of substrates than when the radiorespirometric profile is expressed in actual numerical terms in order to differentiate it from radiorepirometric profiles for other microorganisms. 
     FIGS. 5 and 6 demonstrate how various species of microorganism produce a high level of  14  CO 2  from  14  C-glucose and  14  C-urea, respectively, as opposed to others which produce only low level evolution of  14  CO 2 . Thus, in FIG. 5, all of the organisms set forth in Table 1 were tested under identical conditions against the substrate  14  C-glucose. The failure of P. aeruginosa to produce substantial quantities of  14  CO 2  from this substrate distinguishes it from the 29 other organisms tested. 
     Further, as shown in FIG. 6, testing of all of the organisms set forth in Table 1 against  14  C urea separated the genera of Proteus and Klebsiella from the remainder of the test group. 
     FIG. 7 shows the cumulative evolution of radioactivity from 21 different substrates tested against E. coli. The identifying number to the right of each curve refers to the identification of the substrate set forth in Table 3. Each curve was established by using three data points, one at 15, 30 and 60 minutes. 
     The data obtained for each of FIGS. 5,6,7 and 8 was obtained by adding an inoculum comprising 0.1 ml. or one drop of suspension containing 10 9  cells of the various microorganisms per ml. of suspension. The inoculum was added to 0.1 ml. or one drop of substrate in microculture tray. The mixtures were then covered with getter covers and incubated for the time indicated. The getter covers were then dried and assayed for radioactivity. 
     Incubation time does not appear to be a critical factor. As shown in FIG. 7, most substrates produced similar results after 15 minutes as obtained after 60 minutes. However, the timing of tests for unknown is preferably about the same as used to establish standard radiorespirometric profiles. 
     FIGS. 8 and 9 illustrate the variations which may occur in repeating assays for organisms against a number of different substrates. FIG. 8 shows the ranges of values obtained for five repetitions of E. coli assayed against each substrate after one hour of incubation, and FIG. 9 shows the ranges of values obtained for 12 repetitions of the bacterium P. vulgaris assayed after one hour of incubation against the various substrates. 
     Table 3 gives the radiorespirometric results obtained on 29 species of microorganisms. In this table the substrate is identified in the left hand column by the numbering code used in Table 2. The results set forth in Table 3 were obtained by inoculating the various substrates contained in wells of a microculture tray with one drop of an inoculum containing the microorganism, the suspension having an optical density of about 1 as measured on a spectrophotometer. The inoculum was added to one drop of each substrate and the mixture was covered with a getter cover containing Ba(OH) 2  and incubated for 1 hour. The getter covers were then dried and assayed for radioactivity. Several repetitions for each organism were run against the various substrates. The highest and lowest values obtained for each organism on each substrate are set forth in Table 3. Thus, Table 3 sets forth radiorespirometric profiles for each of these 29 species of microorganisms. 
     
                       Table 3                                                     
______________________________________                                    
       Escherichia  Alkalscens   Shigella                                 
Sub-   coli         Dispar       dysenteriae                              
strate 1 hr (cpm)   1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7      &lt;10     18             &lt;10          &lt;10                            
10     170     1,400    320   400    230   460                            
18     &lt;10     12             &lt;10          &lt;10                            
19     460     4,700    2,200 5,000  &lt;10   21                             
20     4,500   9,400    950   2,800  29    60                             
21     180     400      140   320    180   260                            
22     2,900   11,000   5,000 7,200  350   440                            
23     39      230      420   850          &lt;10                            
24     &lt;10     30       &lt;10   64           &lt;10                            
25     24      370      62    490    &lt;10   26                             
26     &lt;10     56       &lt;10   280          &lt;10                            
27     5,600   11,000   2,900 6,600  320   610                            
28     &lt;10     12       &lt;10   25           &lt;10                            
29     6,000   12,000   5,200 7,800  4,700 8,600                          
30     4,500   8,600    5,100 6,000  6,000 8,200                          
31                                         &lt;10                            
32     5,000   9,000    3,800 6,200  1,400 4,600                          
33     7,900   22,000   11,000                                            
                              20,000 12,000                               
                                           14,000                         
34     5,200   14,000   150   200    48    170                            
35     4,600   7,400    4,200 5,100  300   590                            
38     330     12,000   4,600 11,000 8,500 16,000                         
39     1,700   12,000   4,500 8,400  4,500 11,000                         
40     1,600   11,500   3,200 5,000  210   230                            
41     3,200   17,000   3,600 8,000  8,000 8,600                          
42     300     380      270   450                                         
43     280     420      3,900 6,200                                       
44     6,600   9,300    5,000 6,200                                       
47     66      88       5,200 8,000                                       
48     60      85       380   400    500   550                            
49     150     850      160   240    240   270                            
50     34      140      36    58     20    36                             
51     14      120      62    68     17    30                             
52     340     660      260   530    200   270                            
53     1,900   7,200    2,600 3,200  1,800 2,700                          
54     140     220      62    140    170   200                            
55     5,200   14,000   4,000 5,900  1,900 2,000                          
56                                                                        
57     290     1,000    140   260    860   1,000                          
58     110     260      22    64     400   430                            
59     3,500   10,500   1,600 2,100  1,500 2,600                          
60     3,500   4,800    2,600 3,200  510   630                            
61     170     1,100    6,300 6,900  550   750                            
62     25      340      38    68     92    140                            
63     36      170      19    63     23    35                             
64     180     1,200    32    42     280   480                            
65                                                                        
66                                                                        
67                                                                        
73     940     1,400                                                      
74     1,600   3,000                                                      
75                                                                        
76                                                                        
       Shigella     Shigella     Salmonella                               
Sub-   flexneri     sonnei       choleraesuis                             
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7              &lt;10            &lt;10          &lt;10                            
10     400     500      460   520    400   500                            
18             &lt;10            &lt;10    5,700 7,400                          
19             &lt;10      1,000 2,100  500   1,600                          
20     41      60       5,300 6,600  1,800 4,400                          
21     20      230      180   190    &lt;10   18                             
22     3,300   5,200    5,500 6,200  3,700 8,500                          
23             &lt;10      60    72     37    84                             
24             &lt;10      16    47           &lt;10                            
25     70      170      90    180    800   1,100                          
26     &lt;10     26       36    41     &lt;10   21                             
27     3,700   7,600    5,900 6,700  2,200 6,500                          
28             &lt;10            &lt;10    &lt;10   18                             
29     6,400   7,900    7,300 11,000 6,000 7,000                          
30     5,100   9,000    7,900 11,500 7,000 11,000                         
31                                                                        
32     5,700   6,000    4,900 10,500 3,800 7,400                          
33     13,000  15,000   11,000                                            
                              18,000 11,000                               
                                           20,000                         
34     140     180      2,200 2,300  8,000 15,000                         
35     3,800   11,000   12,000                                            
                              16,000 5,200 8,100                          
38     8,000   14,000   14,000                                            
                              16,000 11,000                               
                                           12,000                         
39     8,100   8,800    9,000 11,000 8,600 16,000                         
40     950     1,400    2,200 4,700  7,200 8,100                          
41     5,800   6,400    7,800 9,500  11,000                               
                                           12,000                         
42     180     190      660   880    400   460                            
43     6,000   6,500    7,200 8,400  8,900 14,000                         
44     6,300   6,600    7,600 12,000 6,100 8,000                          
47     9,500   10,000                12,000                               
                                           19,000                         
48     450     530      410   820    430   540                            
49     250     620      75    160    78    120                            
50     330     420      32    140    54    71                             
51     40      60       13    82     15    50                             
52     880     3,300    580   1,800  270   800                            
53     1,900   2,700    2,000 5,600  2,300 3,300                          
54     130     160      95    230    110   140                            
55     2,500   4,700    5,400 8,900  7,000 8,300                          
56                      16    82     51    53                             
57     450     750      90    270    38    140                            
58     100     160      68    120    30    61                             
59     1,400   1,800    540   3,600  270   900                            
60     130     140      74    170    35    50                             
61     1,200   1,300    2,300 4,400  95    140                            
62     27      55       24    98     13    41                             
63     12      38       10    36     &lt;10   35                             
64     260     320      430   1,100  85    120                            
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
       Salmonella   Salmonella   Edwardsiella                             
Sub-   pullorum     galinarum    tarda                                    
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
 Code #                                                                   
       Low     High     Low   High   Low  High                            
______________________________________                                    
7              &lt;10            &lt;10         &lt;10                             
10     130     290      120   190    450  600                             
18     8,100   9,300    800   1,100  2,800                                
                                          11,000                          
19     41      98       420   500    400  1,500                           
20     21      65       600   700    2,100                                
                                          4,700                           
21     260     280      350   470    310  470                             
22     11,000  12,000   8,000 9,000  7,000                                
                                          9,500                           
23     15      75       54    92     1,600                                
                                          2,000                           
24     &lt;10     31       &lt;10   27     &lt;10  70                              
25     110     330      160   180    22   75                              
26     &lt;10     39       60    150    &lt;10  56                              
27     850     1,200    9,500 11,000 260  430                             
28     &lt;10     30       &lt;10   18          &lt;10                             
29     1,100   1,400    1,100 4,600  2,200                                
                                          4,200                           
30     1,300   1,700    11,000                                            
                              14,000 170  760                             
31                                                                        
32     1,100   1,400    10,000                                            
                              18,000 840  3,700                           
33     300     380      880   950    560  13,000                          
34     910     1,100    8,200 10,500 9,000                                
                                          12,000                          
35     680     780      350   420    850  5,200                           
38     1,200   1,700    9,700 13,000 11,500                               
                                          14,000                          
39     1,200   1,700    5,300 13,000 7,500                                
                                          12,000                          
40     230     430      4,100 8,100  2,900                                
                                          12,000                          
41     1,000   1,700    10,000                                            
                              17,000 9,000                                
                                          14,000                          
42     620     690      310   460    3,400                                
                                          4,500                           
43     710     1,300    1,500 2,700  7,000                                
                                          8,000                           
44     1,300   1,500    12,000                                            
                              15,000 9,500                                
                                          11,000                          
47                                                                        
48                      380   2,800  4,500                                
                                          5,600                           
49                                   580  650                             
50                                   81   95                              
51                                   51   71                              
52                                   210  250                             
53                                   1,100                                
                                          1,200                           
54                                   55   74                              
55                                   1,600                                
                                          2,600                           
56                                                                        
57                                   170  230                             
58                                   35   95                              
59                                   150  210                             
60                                   52   58                              
61                                   73   96                              
62                                   42   48                              
63                                   12   42                              
64                                   5,800                                
                                          9,900                           
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
                    Citrobacter  Klebsiella                               
Sub-   Arizona      freuendii    pneumonia                                
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low  High                            
______________________________________                                    
7      &lt;10     35             &lt;10    12   37                              
10     110     520      150   600    350  1,200                           
18     350     5,300    4,800 12,000 510  1,400                           
19     95      8,200    5,000 16,000 1,900                                
                                          5,400                           
20     280     2,900    1,500 5,900  1,300                                
                                          3,700                           
21     80      330      62    210    2,100                                
                                          5,000                           
22     380     7,200    2,100 6,000  4,100                                
                                          6,200                           
23     160     4,200    950   4,200  850  1,400                           
24     &lt;10     45             &lt;10         &lt;10                             
25     70      350      130   420    120  720                             
26     15      450      210   950    15   92                              
27     400     4,800    2,700 6,200  3,200                                
                                          13,000                          
28     &lt;10     35             &lt;10    &lt;10  36                              
29     500     8,500    4,700 8,200  2,100                                
                                          7,500                           
30     1,800   8,500    4,100 9,200  3,500                                
                                          7,500                           
31                                                                        
32     1,300   8,500    5,800 11,000 4,800                                
                                          8,500                           
33     3,300   24,000   8,000 20,000 8,800                                
                                          15,000                          
34     290     5,500    5,100 9,600  7,200                                
                                          9,000                           
35     1,900   15,000   3,100 13,000 850  4,000                           
38     610     9,500    1,900 14,000 4,000                                
                                          16,000                          
39     1,400   12,000   5,800 8,800  7,500                                
                                          12,000                          
40     250     12,000                3,400                                
                                          9,000                           
41     1,500   8,000                 4,500                                
                                          8,000                           
42                                   580  750                             
43                                   6,500                                
                                          9,000                           
44                                   6,000                                
                                          7,000                           
47     6,500   8,000    5,800 6,200  8,800                                
                                          15,000                          
48     4,000   5,500    2,000 3,400  3,200                                
                                          12,000                          
49     380     700      250   450    380  18,000                          
50     110     600      88    150    310  950                             
51     14      52       &lt;10   32     &lt;10  24                              
52     800     1,500    75    27     900  1,200                           
53     2,000   5,500    2,100 2,600  3,800                                
                                          5,700                           
54     320     1,400    620   2,600  420  1,200                           
55     6,000   10,000   3,100 5,800  2,400                                
                                          9,400                           
56                                                                        
57     410     620      170   320    4,200                                
                                          1,800                           
58     850     550      40    100    32   520                             
59     3,200   4,300    2,100 3,200  2,100                                
                                          4,700                           
60     3,200   7,000    3,200 6,800  6,000                                
                                          11,000                          
61     2,300   6,200    5,200 8,500  1,900                                
                                          5,500                           
62     38      450      51    330    100  800                             
63     18      29       16    72     240  550                             
64     120     390      450   2,700  92   170                             
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
       Klebsiella   Klebsiella   Enterobacter                             
Sub-   ozaenae      rhinoschleromatis                                     
                                 cloacae                                  
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code 190                                                                  
       Low     High     Low   High   Low  High                            
______________________________________                                    
7              &lt;10            &lt;10         &lt;10                             
10     310     330      32    42     380  420                             
18             &lt;10      &lt;10   16     4,100                                
                                          6,200                           
19     3,200   5,100    34    65     4,000                                
                                          5,500                           
20     500     980      2,100 2,500  2,000                                
                                          2,300                           
21     81      170      180   230    3,400                                
                                          5,000                           
22     4,000   4,600    4,700 6,500  5,500                                
                                          8,500                           
23     1,100   2,300    140   160    410  1,400                           
24             &lt;10      &lt;10   27     &lt;10  16                              
25     45      68       140   210    90   420                             
26     34      36       50    75     &lt;10  63                              
27     1,200   1,900    4,500 5,200  3,500                                
                                          7,500                           
28     160     950            &lt;10    32   75                              
29     4,800   5,200    3,200 3,700  4,600                                
                                          6,500                           
30     4,500   9,500    200   250    5,500                                
                                          7,500                           
31                                                                        
32     5,500   7,400    5,000 9,000  5,500                                
                                          7,500                           
33     12,000  22,000   5,000 15,000 10,000                               
                                          14,000                          
34     9,000   12,500   9,200 12,000 5,500                                
                                          8,000                           
35     12,000  15,000   6,200 7,500  6,200                                
                                          7,000                           
38     11,000  12,000   9,500 11,000 7,800                                
                                          12,000                          
39     10,000  12,000   7,500 14,000 8,000                                
                                          9,100                           
40     7,500   9,500    6,000 6,500  6,100                                
                                          6,700                           
41     7,000   12,000   8,800 12,000 10,000                               
                                          11,000                          
42     1,600   2,700    340   410    2,400                                
                                          2,600                           
43     5,100   9,500    6,200 10,000 8,800                                
                                          9,000                           
44     6,600   11,000   8,000 9,000  7,000                                
                                          7,500                           
47                                   7,000                                
                                          11,000                          
48     5,200   10,000   4,100 4,800  3,200                                
                                          7,800                           
49     410     730      300   740    310  1,200                           
50     410     800      45    170    1,200                                
                                          6,500                           
51     35      65       32    85     &lt;10  700                             
52     320     590      1,100 1,500  480  1,500                           
53     520     830      1,800 2,800  3,000                                
                                          9,500                           
54     150     300      58    120    200  8,100                           
55     650     950      4,500 6,400  4,200                                
                                          11,000                          
56     180     220                                                        
57     310     420      130   400    3,300                                
                                          28,000                          
58     100     170      48    130    780  1,300                           
59     2,200   5,700    3,300 5,600  1,700                                
                                          4,100                           
60     5,800   7,000    35    150    2,100                                
                                          12,000                          
61     1,200   1,800    1,500 2,000  2,300                                
                                          4,900                           
62     60      180      58    92     2,100                                
                                          7,200                           
63     33      65       40    82     780  2,200                           
64     280     350      110   200    320  580                             
65                                                                        
66                                                                        
67                                                                        
73                                                                        
75                                                                        
75                                                                        
76                                                                        
       Enterobacter Enterobacter Enterobacter                             
Sub-   aerogenes    hafnia       liquefaciens                             
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7              &lt;10            &lt;10          &lt;10                            
10     170     510      1,400 2,900  180   500                            
18     5,800   12,000   100   520    2,900 8,000                          
19     4,000   11,000   780   1,100  4,000 7,800                          
20     1,900   2,100    1,500 1,800  2,400 3,800                          
21     2,100   2,700    88    220    150   230                            
22     5,100   6,600    550   680    5,800 7,000                          
23     3,100   5,000    920   1,400  1,100 3,700                          
24     &lt;10     20             &lt;10    &lt;10   61                             
25     13      28       &lt;10   17     160   500                            
26     11      56       &lt;10   2      51    140                            
27     3,200   7,500    20    1,200  1,900 4,400                          
28     550     600      450   700    320   1,300                          
29     3,000   9,000    7,000 8,000  5,500 9,500                          
30     4,700   9,500    4,100 8,200  5,500 9,500                          
31                                                                        
32     6,000   11,000   4,800 7,200  7,500 12,000                         
33     11,000  19,000   8,500 17,000 13,000                               
                                           18,000                         
34     4,800   9,800    4,700 5,200  5,300 12,000                         
35     2,400   11,000   2,200 8,500  2,500 4,100                          
38     5,400   10,000   8,100 11,000 7,100 13,000                         
39     5,500   11,000   6,800 7,700  8,200 11,000                         
40     10,000  11,000   9,000 9,500  5,000 9,500                          
41     11,000  12,000   4,400 7,500  8,000 12,000                         
42                      5,100 5,500  4,500 6,200                          
43                      5,100 5,500  6,800 9,500                          
44                      7,200 7,500  7,400 9,000                          
47                      9,900 10,500                                      
48     3,800   5,600    3,200 7,800  506   900                            
49     880     960      4,800 9,600  560   950                            
50     210     460      1,200 5,300  460   730                            
51     23      40       30    52     31    67                             
52     210     480      320   1,100  310   350                            
53     260     380      2,100 3,500  1,200 1,700                          
54     320     400      600   900    300   450                            
55     9,500   11,000   4,400 9,500  4,200 7,000                          
56     25      36                    320   420                            
57     110     220      1,800 3,000  230   430                            
58     43      73       130   590    60    180                            
59     2,100   3,600    4,500 8,500  3,200 9,500                          
60     2,500   4,500    60    3,400  2,700 5,200                          
61     950     2,700    950   3,000  750   1,200                          
62     15      59       50    390    42    580                            
63     12      31       120   270    31    280                            
64     550     620      380   1,100  410   490                            
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
       Pectobacterium                                                     
                    Serratia     Proteus                                  
Sub-   carotovarum  marcescens   vulgaris                                 
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7              &lt;10            &lt;10    220   9,000                          
10     850     950      230   420    95    350                            
18     8,500   13,000   4,300 5,100  350   7,500                          
19     95      140      3,500 4,000  18    85                             
20     65      120      3,500 4,000  310   1,600                          
21     6,100   6,800    3,500 4,800  2,200 8,500                          
22     8,000   9,000    6,300 8,200  3,800 7,800                          
23     &lt;10     22       850   1,800  &lt;10   58                             
24     28      88             &lt;10    &lt;10   65                             
25     180     270      160   330    &lt;10   110                            
26     60      70             &lt;10    &lt;10   220                            
27     5,500   8,000    3,500 8,000  &lt;10   60                             
28     &lt;10     32       150   600    &lt;10   45                             
29     650     700      6,500 7,000  310   1,700                          
30     900     1,000    5,000 7,000  290   900                            
31                                                                        
32     620     920      5,800 8,000  2,500 9,500                          
33     12,000  13,000   11,000                                            
                              17,000 32    250                            
34     9,000   11,000   5,500 12,000 1,600 8,500                          
35     1,800   2,600    2,200 6,800  1,100 6,200                          
38     7,000   8,000    3,100 7,500  8,500 17,000                         
39     4,800   6,200    6,500 10,500 7,200 17,000                         
40     2,300   2,600    5,500 6,000  3,800 13,000                         
41     12,000  18,000   8,500 13,000 4,500 16,000                         
42     500     600      5,800 6,200                                       
43     500     600      8,000 9,000                                       
44     11,000  14,000   8,000 9,000                                       
47                      9,000 10,000 5,000 6,000                          
48     1,100   3,100    4,800 9,800  320   850                            
49     280     390      3,909 9,200  180   700                            
50     78      120      1,800 2,700  45    550                            
51     35      65       &lt;10   52     &lt;10   16                             
52     950     2,700    220   800    50    250                            
53     1,600   3,300    380   600    260   650                            
54     70      100      260   550    550   360                            
55     2,800   3,100    3,200 9,000  11,000                               
                                           14,000                         
56     250     460                                                        
57     150     220      1,100 2,800  500   4,000                          
58     55      120      40    100    85    200                            
59     7,500   9,000    5,700 9,500  1,800 3,900                          
60     850     1,300    9,200 20,000 700   1,500                          
61     170     180      1,100 5,000  120   250                            
62     35      64       41    180    55    1,800                          
63     25      39       52    350    &lt;10   45                             
64                      800   6,000  85    370                            
65                                   500   700                            
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
       Proteus      Proteus      Proteus                                  
Sub-   mirabilis    rettgeri     morganii                                 
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7      150     290      550   850    320   2,100                          
10     310     700      210   270    350   620                            
18     630     750      5,000 6,000  510   1,400                          
19     30      280            &lt;10    19    51                             
20     78      120      20    45     35    52                             
21     320     360            &lt;10    &lt;10   20                             
22     5,200   5,800    4,000 6,000  3,900 7,100                          
23     &lt;10     15             &lt;10          &lt;10                            
24     18      52             &lt;10          &lt;10                            
25     48      63       &lt;10   21     16    28                             
26     58      62       &lt;10   26     &lt;10   62                             
27     &lt;10     140      220   410    240   260                            
28             &lt;10      &lt;10   61           &lt;10                            
29     6,500   12,000   300   350    1,900 2,000                          
30     7,500   10,500   4,000 5,500  3,100 5,100                          
31                                                                        
32     7,500   9,000    950   1,900  1,200 1,400                          
33     13,000  19,000   12,000                                            
                              13,000 12,000                               
                                           14,000                         
34     4,000   7,100    5,600 7,400  420   510                            
35     3,500   5,500    16    22     5,200 7,200                          
38     8,500   9,500    6,600 9,000  3,700 5,200                          
39     6,000   8,000    6,000 7,000  850   3,300                          
40     1,400   1,500    4,000 6,500  5,800 6,200                          
41     9,000   21,000   8,000 9,800  5,800 7,000                          
42     850     900      1,500 2,500  700   2,000                          
43     9,500   10,000   2,500 3,500  4,000 4,800                          
44     8,000   9,000    8,000 8,800  6,500 7,500                          
47                      9,500 11,000 8,000 9,000                          
48     650     780      1,100 4,700  280   450                            
49     65      150      450   1,500  75    270                            
50     21      90       240   850    120   480                            
51     &lt;10     21       51    520    12    33                             
52     13      280      210   700    120   530                            
53     230     1,600    2,900 4,100  1,400 2,300                          
54     140     580      160   1,600  140   3,100                          
55     5,000   11,000   6,500 9,200  5,000 8,800                          
56     2,400   2,800    60    1,600  1,000 1,600                          
57     230     310      85    4,500  220   580                            
58     16      110      100   1,600  &lt;10   160                            
59     1,900   3,300    1,700 4,000  2,200 5,000                          
60     12      85       380   2,600  270   1,700                          
61     1,800   8,500    600   960    75    720                            
62     900     2,600    96    2,100  16    1,300                          
63     1,100   2,900    35    550    &lt;10   920                            
64     650     1,900    610   750    34    750                            
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
       Providence   Providence   Pseudomonas                              
Sub-   stuartii     alcalifacens aeruginosa                               
______________________________________                                    
strate 1 hr. (cpm)  1 hr. (cpm)  1 hr. (cpm)                              
Code # Low     High     Low   High   Low   High                           
______________________________________                                    
7                             &lt;10          &lt;10                            
10                      350   420    370   390                            
18                      4,800 6,200  1,600 3,800                          
19                      40    75     5,000 6,600                          
20                      45    95     100   1,600                          
21                      65    700    210   230                            
22                      2,500 4,500  1,900 2,700                          
23                            &lt;10    2,700 4,800                          
24                            &lt;10    &lt;10   28                             
25                      31    80     90    100                            
26                            &lt;10    22    56                             
27                      250   300    65    8,500                          
28                      &lt;10   18     3,500 4,000                          
29                      2,300 7,600  5,400 6,600                          
30                      1,100 3,600  8,000 9,400                          
31                                                                        
32                      1,200 6,200  8,000 12,000                         
33                      9,200 11,000 5,000 9,400                          
34                      5,700 14,000 6,100 11,000                         
35                      48    140    4,500 5,500                          
38                      12,000                                            
                              14,000 5,000 11,000                         
39                      8,500 11,000 5,800 10,500                         
40                      6,300 16,000 880   2,200                          
41                      13,000                                            
                              15,000 8,200 11,000                         
42                                   7,600 8,300                          
43                                   5,600 6,000                          
44                      7,500 8,000  8,800 9,200                          
47                      14,000                                            
                              15,000 8,000 10,000                         
48                      4,400 6,200  1,200 1,600                          
49     750     900      520   1,000  1,300 1,600                          
50     120     130      160   390    1,900 2,200                          
51     180     220      210   370    28    58                             
52     380     450      170   1,100  100   150                            
53     2,800   3,200    5,400 16,000 220   280                            
54     400     450      280   3,200  210   240                            
55     6,700   7,400    3,000 6,200  3,100 3,700                          
56                                                                        
57     260     480      1,300 5,600  2,800 4,000                          
58     110     180      11,000                                            
                              22,000 210   250                            
59     5,800   6,200    11    22     1,300 1,400                          
60     120     160      350   740    5,800 6,200                          
61     570     950      16    280    1,500 4,000                          
62     140     180      80    110    90    230                            
63     62      90       26    300    700   2,200                          
64     140     180      120   180    420   720                            
65                                                                        
66                                                                        
67                                                                        
73                                                                        
74                                                                        
75                                                                        
76                                                                        
______________________________________                                    
 
    
     The following example illustrates the procedure for the identification of pathogenic bacteria by the radioisotopic identification technique of this invention: 
     EXAMPLE 
     A sample of a human stool is received in the laboratory. The history of the patient indicates the possibility of a Salmonella infection. The sample material is streaked onto agar plates including Eosine Methylene Blue Agar, MacConkey Agar, Blood agar, Bismuth Sulfite Agar, Salmonella Shigella agar and Selenite-F Broth. Each inoculated media is then incubated at 35° C. overnight. The next day, the plates are observed and some are found to show bacterial colonies which have the appearance of salmonella. Several typical colonies are picked from the agar plates with a swab and suspended in a saline solution. The cell density is adjusted to an optical density of approximately 1 as determined by a spectrophotometer. About 0.05 ml. of the cell suspension is added dropwise to each well in a microculture tray. Each well on the tray contains 0.05 microcuries of a different one of the following  14  C labeled substrates identified by the code numbers set forth in Table 2: 7, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 30, 33, 34, 35, 40, 42, 43, 44, 47, 50, 53, 55, 57, 58, 59, 60, 61, 62, 63. The inoculated microculture tray is covered with a sheet impregnated with Ba(OH) 2 , the portion of the cover overlaying each well being coded so as to identify the substrate in that well. The tray is incubated for one hour and the Ba(OH) 2  cover is removed and dried under a heat lamp. The microculture tray is discarded into a receptacle for containing radioactive waste materials. The dried Ba(OH) 2  containing pad is measured for radioactivity and the counts per minute corresponding to each  14  C labeled substrate is automatically recorded. There is thereby obtained a radiorespirometric profile of the unknown sample material. This profile is compared to standard radiorespirometric profiles of the organisms set forth in Table 1. Comparison is performed by means of a computer which tests the goodness of fit and statistical reliability. The radiorespirometric profile of the unknown organism is found to compare to the standard radiorespirometric profile of the organism  Salmonella typhi. 
     The steps performed on the first day, i.e., the streaking of the sample material on the agar plates followed by overnight incubation, are required by either the conventional or the radiorespirometric indentification technique of this invention. However, the steps performed on the second day for the radioresperometric technique do not require highly experienced personnel which are required by conventional identification techniques since the interpretation of results is not required--i.e., the identification is made automatically. Moreover, the time required to perform the steps on the second day of the radiorespirometric identification technique is about five minutes manipulation time and approximately one hour and 10 minutes total elapsed time which is considerably less than the day or more required by conventional identification techniques. 
     There will now be described apparatus for collecting and analyzing data relating to a plurality of samples of organisms or the like. A suitable incubation unit assembly for use with an automatic analyzing system is shown in FIGS. 10 and 11 and includes a culture tray 20 having a plurality of generally hemispherical depressions 21 spaced in a regular array of columns and rows throughout the body of the tray. While the tray can be produced as a solid, self-supporting unit similar to that shown in FIGS. 2-4, a relatively inexpensive, disposable and yet equally suitable apparatus can be produced by vacuum forming the tray from a relatively thin sheet of a thermo-formable plastic material. The tray is then designed for use with a reusable support body such as that indicated generally at 23, the support body being relatively thick and rigid and having a plurality of wells 24 spaced in the same array as in tray 20. The upper surface of body 23 is provided with an alignment pin 25 which is designed to pass through an opening 26 provided in tray 20 so that the apparatus will be in proper orientation as well as alignment. The lower surface of body 23 is provided with a plurality of downwardly protruding parallel ribs 27 which extend substantially the length of body 23 and are intended to perform a spacing function during incubation, as will be described. 
     The apparatus also includes a collection material cover unit indicated generally at 29 which includes a backing member 30 and an absorbent material sheet 31 which constitutes the CO 2  collector previously described. The backing member 30 is a relatively stiff plastic member which is generally planar in configuration but which is provided with downwardly extending edges 33 and 34 which serve as stiffeners and as spacers in the analysis system to be described. 
     As seen in FIG. 11, when the materials are inserted into depressions 21 and the collector material in cover 29 is placed thereon, the assembly constitutes a relatively thin, easily manageable structure in which the cover forms a tight seal over each of the depressions, isolating each such depression from each other depression and from the external atmosphere. 
     During the incubation period a plurality of such assemblies can be stacked one upon the other as shown in FIG. 12. In that figure, each assembly is spaced from each lower assembly by the downwardly extending ribs 27 to permit the passage of air, thereby maintaining a uniform temperature environment for each incubation unit, regardless of its position in the stack. A weight 35 is placed on the cover 29 of the topmost unit to be sure that the cover of that unit, and all lower units, is tightly covering the depressions in the respective trays 20. Each body 23 can be provided with a legend indicating the time when the incubation for that specific tray is to be terminated so that it can be removed at the appropriate time for further processing and identification procedures. 
     It will also be observed that the ribs 27, being rather uniformly disposed across the width of each body 23, apply rather uniform pressure to the cover 29 of the unit below it, and that, furthermore, the ribs are disposed beneath rows of wells so that the cover of the unit on which the ribs press is pressed against the well openings, i.e., at exactly the position where pressure is most needed. 
     As previously described, after the incubation period has transpired the covers are removed and analyzed for level of radioactive material in the specific regions covering the wells. A particularly advantageous apparatus for accomplishing this analysis will now be described. 
     It will be observed, preliminarily, that a cover such as that described for use with the apparatus of FIGS. 10-12 will be that as shown in FIG. 13 wherein a cover 29 is provided with an absorbent layer 31, this being seen from the undersurface or in an inverted position in FIG. 13. The cover is also provided with an alignment hole 28 for alignment with the bodies supporting the material to be analyzed. 
     The apparatus to be described, however, is also capable of handling and analyzing materials which have been exposed in a different fashion, specifically in the form of separable pads which can be exposed to a culture and then placed in the cover. For this purpose, a cover of the type shown in FIG. 14 is provided, this constituting a relatively rigid shallow U-shaped tray 40 which is provided with a plurality of depressions 41 to receive pads of absorbent material 42 which are to be investigated. The depressions 41 are shallow and circular and are arranged in regular rows and columns, preferably in the same kind of array employed with depression 24 in body 23 or wells 21 in the culture tray 20 described with reference to FIGS. 10 and 11. Using the same array permits analysis with the same equipment. 
     An automatic apparatus for analyzing the material on the covers is shown in FIG. 15 in a general and schematic fashion. A plurality of covers 45 are stacked one upon the other immediately above a continuous conveyor belt 46. The covers are maintained in aligned position possibly as shown in FIG. 15 between upstanding posts 47. The covers are maintained in spaced relationship by the edges thereof, as shown at 33 and 34 in FIG. 11. It will be observed that the covers can be of the form shown in FIG. 13 or of the form shown in FIG. 14. 
     A source of hot air 48 is provided in the vicinity of the covers to pass air between the covers, thereby rendering them in a dry state. 
     The conveyor 46 is provided with sets of upwardly extending lugs in pairs as shown at 50, 51 and 52. The pairs of lugs are spaced apart by distances greater than the length of a cover. When a set of lugs such as 51 arrives at the bottom of one of covers 45, the lugs engage the rear edge of the cover and move it along with the belt past the analyzing apparatus, after which the cover is dropped or removed from the end of the conveyor and either discarded, returned to the input end for a repeat run, or cleaned and prepared for further use. 
     The analyzing apparatus which is broadly illustrated in FIG. 15 includes a plurality of sensitive detectors indicated generally at 55, these detectors being selected for sensitivity to the specific kind of radioactivity to which the regions of absorbent material 31, or pads 42 have been exposed. In particular, it is contemplated that Geiger-Muller detectors are to be employed and that the number of such tubes is equal to the number of regions in the width of the covers to be inspected. Additionally, the tubes are in the same array as one row of those regions and as one row of wells 21 in sample tray 20. 
     Detectors 55 produce electrical signals representative of the counts of radioactive particles emitted from the specific regions under examination and those signals are then transmitted over conductors indicated generally at 56 to a data processing and display unit 57 which will be described in greater detail. Generally speaking, however, the data processing apparatus receives the count information from the detectors, compares it with a library of known information describing previously identified material and produces a display, such as a printout, identifying the detected material as one previously identified or indicating that no such valid comparison has been made. 
     In order for the process of detection and analysis to be properly conducted, it is desirable that each set of regions be moved to a position directly adjacent the detectors 55, be retained in that position for a predetermined interval of time and then moved. It is also desirable that the counters be controlled to read and reset at the beginning and end of each such count, transmitting the count at the reset time. The control of conveyor 46 and the counter is synchronized and performed by a control unit 58 which will also be described in greater detail. Control unit provides the energization of a drive motor 59 and a drive motor 60 which provide the motivating force for conveyor belt 46. 
     FIG. 16 shows, in a block schematic diagram form, an apparatus usable in the data processing device referred to in FIG. 15 and used to perform the automatic method of the invention in conjunction with the conveyor and analysis apparatus disclosed therein. A plurality of particle detectors are indicated generally at 55, each of these being connected to a source of D.C. voltage which is conventionally required, the voltage being a relatively high voltage in the case of the usual Geiger-Muller tubes. One such tube and the apparatus used therewith will be described in detail. The remaining tubes are provided with substantially identical processing channels. 
     Each tube includes an envelope 65 which contains an ionizable gas, the envelope surrounding an electrode 66 connected to one terminal of the D.C. source 67. The other terminal of the source is connected to an electrode 68 which extends into the ionizable gas and detects the avalanche ionization activity indicative of the exposure of the device to a particle. Each such activity generates a pulse electrical output which is coupled through a capacitor 69 to the input of a conventional amplifier 70 which can be employed to strengthen the signal and, if desired, to perform a shaping function. 
     The output of amplifier 70 is connected through an AND gate 71 to the input of a counter 72 which receives the pulses gates through from amplifier 70 and accumulates a count thereof. The output of the counter can be transferred to a buffer storage unit 74 for temporary storage of the count, rendering it available to further processing apparatus. 
     A drive control unit 58 operates in conjunction with a sequence control or multiplying apparatus 75 and includes timing devices to activate the various portions of the system in proper order. As described previously in connection with the method of the present invention, it is desirable to accumulate a count representative of the mean rate of emission of particles from each region of the absorbent material being investigated. Thus, it is necessary to control the interval of time during which each tube is exposed to each specific region from which a radiation count is to be obtained. This interval is controlled by AND gate 71 and the input to the AND gate on conductor 73, which input is provided from control circuitry within control unit 58. That control unit opens gate 71, permitting pulses to be delivered to the counters only during the predetermined interval. 
     Control unit 58 also provides signals to the sequence selector or multiplexor 75 to permit the sequence selector to transfer accumulated count information from the buffer 74 and the similar buffers associated with the other Geiger-Muller tubes in the sensor array, the counts being individually provided to a computer 76 which further processes the information and provides a usable result. The function of the sequence selector is to provide the accumulated counts in an established, ordered sequence so that they can be further analyzed. If necessary, the count selected by the sequence selector can be provided to a translator 77, the function of which is recognizable by the computer. The transmitted information is then inserted into a store 78 within the computer and it is compared with previously stored information contained in a data file library 79, the comparison being accomplished in a word comparator 80. The results of the comparison, including the identification of all matches occurring between the data in store 78 and library 79, is printed or otherwise displayed in a read out unit 81 of conventional nature. The comparison operation and the control of the library scan and coordination of these operations with the sequencer are accomplished by an internal control unit 82 which provides control signals and receives accomplishment feedback signals from the comparison unit, the library and control unit 58. 
     As previously indicated, the analysis system described herein is capable of performing analysis of various types. In order for the data processing apparatus to appropriately function, it is necessary that reference be made, for example, to the appropriate library, and it is further necessary for the control and comparison apparatus to be provided with appropriate start-up information so that the appropriate libraries can be searched, among other things. To render this aspect of the operation as automatic as possible, each one of covers 45 provided to the unit is identified by a code plate 85 disposed on an edge of each cover. The code plate is a relatively simple device which permits each cover to be readily identified as to test type as well as with other information. One such code plate, and a system of reading the plate usable with the apparatus of FIG. 15, is shown in FIGS. 17-19. In FIG. 17 the edge of a cover 29 is provided with a code plate indicated generally at 85 including a plurality of reflective rectangles 86, each such rectangle being adhered to a release paper backing 87 mounted on cover 29. The rectangles can be formed by scribing line 88 at regular intervals in a continuous reflective strip. While only four rectangles are shown in FIG. 17, it will be apparent that a much larger number of rectangles can be used, depending upon the number of bits required for a specific identification purpose. The entire plate can be removed and replaced for reuse of the cover if desired. 
     The coding operation takes place by simply removing a selected number of the reflective rectangles in specific positions, thereby forming a digital word in which reflective and nonreflective rectangles are established in a specific sequence. The rectangles can be arrayed in this manner in accordance with a preestablished code identifying the operation to be accomplished with that cover. One partly peeled label is shown at 89. If that label were to be removed completely leaving the other three reflective rectangles in place, and if a system is established in which a reflective rectangle represents a binary 1 and the absence thereof indicates a binary zero, the word formed by the removal of rectangle 89 would be 1101. 
     It is contemplated that the code plate would be positioned near the front end of a cover 29 as shown at 85 in FIG. 13. An optical reader housing 90 can then be disposed at one end of a guide rail through which the cover will pass so that the cover code can be read and the information contained therein employed before the Geiger tubes begin to gather data from the regions on the cover. A typical optical apparatus which can be employed to accomplish this function is shown in FIGS. 18 and 19 wherein a housing 90 is mounted on a guide rail 91 and contains a source of light 92, the source of energization for which is conventional and not shown. A photoelectrical cell 93 is also disposed in housing 90, the source and cell being separated by an opaque barrier 94. An opening 95 permits light to emerge from the housing containing source 92 and an opening 96 permits light reflected from code plate 85 to enter the housing and impinge upon cell 93, producing an electrical variation which will be recognized by appropriate photo cell circuitry as the existence of a digital bit. A sequence of such of bits can be provided to control apparatus 58 by conductors 97 as the cover moves past the reader to initiate the necessary control functions. 
     Specifically, assume that code 1101 identifies a cover having regions of collected CO 2  from an unknown organism which has been incubated with a plurality of known substrates 1 through 36 in table. Receipt of code 1101 by control unit 58 will (1) cause that control unit to drive the conveyor past detectors 55 in a stepwise fashion, pausing with each detector over its region for a predetermined interval suitable for that test; (2) indicate to control 82 that the data file set for all count ranges resulting from tests with substrates 1 through 36 should be made available for comparison with count data to be provided to store 78; and (3) activate a subroutine to receive each count in multiplexed sequence from sequencer 75, compare it with each item in the relevant set in the data file, and print out the count and match identification whenever a match occurs, i.e., whenever the count read from a particle detector falls within one of the count ranges in the data file set. 
     This is a relatively simple sequence of events which will yield basis data on which a first sort can be made. In most cases, this data will indicate a number of organisms which the unknown cannot, or probably would not, be, and may also indicate most suitable substrates to use in a second set of tests in a second tray. The second test would follow substantially the same steps as the first except that the code established on plate 85 will indicate to the control unit that a different set of substrates is being employed with the unknown microorganism and that a different data file set is to be used for comparison. This sequence of steps can be repeated, as necessary until a sufficiently accurate match with a sufficiently large number of substrates identifies the organism to a required degree of certainty or specificity. 
     A more sophisticated, more accurate and faster, but somewhat more complex, approach involves the use of the matching and computing capacity of the computer central processing unit (CPU). In this technique, a second data file, which can be a read out only memory, is provided with permutations of matches which identify organisms to various degrees of completeness in accordance with known statistical procedures. The apparatus can then be queried regarding the identity of an organism tested on, for example, a set of six trays with an assortment of substrates, to a probability expressed in sigma functions. The resulting printout will then be programmed to yield each such organism identity, if more than one exist, which satisfy the requested accuracy. 
     While certain advantageous embodiments of the invention have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.