1. Field of the Invention
The invention is concerned with obtaining generally reproducible growth rates for individual micro-organisms upon the surfaces of agar-based gels. More particularly, the invention is concerned with micro-organism growth upon agar-based gels which have a very smooth surface so that surface imperfections do not lead to apparent differences in growth rates of particular micro-organisms grown thereon.
2. Prior Art
The preparation of agar gels for the growth of micro-organisms so as to allow identification of the micro-organisms, identification of particularly effective anti-micro-organism agents thereagainst, and the like is of course very well known. Such agar-based gels must contain therein the essential nutrients for the growth of the particular micro-organism being grown thereon and as is well recognized must be grown in sterilized cells of one nature or another. For example, growth may take place in tubes or very often in petri dishes or the like.
A serious problem which has existed with prior art growth cells, such cells being defined as a container having an agar-based gel therein, has been that the rate of growth of a particular micro-organism on the surface of the gel has often been effected by small or large bubbles which are formed during the mixing of the materials from which the gel is formed and which do not escape fully therefrom during the gelling process. A uniform or more properly a generally reproducible growth rate is necessary for each particular micro-organism if it is to be properly identified and/or the effects of various anti-micro-organism chemicals are to be properly evaluated upon it. Heretofore, in order to obtain such a uniform rate it has been customary in the art when, for example petri dishes, are used and a gel is formed therein which does not have a completely smooth surface, to open the dishes and then quickly flame them to melt slightly the top surface thereof so that any and all depressions and/or hills therein will be smoothed out and the resulting top surface of the gel will be sufficiently smooth so that generally reproducible growth rates will be observed for each micro-organism.
This flaming solution has not proven completely satisfactory for a number of reasons. First, the flaming itself requires reopening of the petri dish or the like thus drastically increasing the chances of contamination from foreign micro-organisms. Second, the flaming is not fully effective if truly large depressions and/or hills have been introduced into the agar-based gel by the bubbles formed therein during mixing of the gel ingredients. Third, the flaming technique even when successful takes up a good deal of valuable time. Fourth, the flaming may lead to a selective destruction or removal of certain essential nutrients from the area of the gel which is directly exposed to the flame. The present invention provides a complete solution to the problem of having uneven surfaces on the top of agar-based gels while completely eliminating the necessity for flaming. This solution also removes the necessity for ever opening the petri dishes or the like which contain the gel therein except for innoculation thereof so that chances of contamination are drastically reduced. Further, the solution of the present invention to the above problems completes the formation of an agar-based gel medium on which micro-organisms will grow at precisely the same rate within experimental error as the same micro-organisms will grow upon prior art agar-based gels having smooth top surfaces as produced for example by bubble free formation of the gels. Further, by use of the technique of the present invention, much more active mixing techniques can be used to form the agar-based solution which is to be gelled thus reducing the time needed to perform such mixing.