[A statistical method for the determination of the yield correlation of antibiotic-producing microorganisms].
The antibiotic yields of industrial selectants must be checked at several steps of cultivation. Here the question arises whether the activities at the different levels of cultivation are correlated. The common coefficient of correlation cannot be used because repeated determinations of the yield at one selectant result in different values. In order to have only one fixed value per selectant we define the mean value around which the observed values are varying. But these mean values cannot be observed. Thus, an adequate method of correlation similar to that in Guiard and Herrendörfer (1977) was used. The method is demonstrated in two examples: With selectants of Streptomyces noursei for streptothricin titers in 20 ml- and 20 l-cultures as well as with selectants of Penicillium chrysogenum for potency indices in surface cultures and penicillin titers in 50 ml submerged cultures, respectively. In both cases the coefficients of correlation were above 0.7.
Correlation and Linear Regression if the Random Variables are Subject to Errors or Fluctuations
For the model x=a+e, y=b+d estimators of Pearson's coefficient of correlation and of the line of regression between a and b are presented. The problem of prediction is dealt with.
Rapid Method for Determining the Minimum Inhibitory Concentration of Ampicillin for Haemophilus influenzae
A rapid method for determining the minimal inhibition concentrations (MICs) of ampicillin using Haemophilus influenzae as the test organism is described. This semiautomated technique using the Autobac system was compared with the agar dilution MIC method. Fifty-seven isolates of both susceptible and resistant H. influenzae were tested. There was exact quantitative agreement with 65% of the isolates, and 91% of the isolates showed no more than a one-dilution-interval difference when MICs were determined by both methods. Total testing time was 3 to 4 h.