THE EFFECT OF SUBMINIMAL INHIBITORY CONCENTRATIONS OF PENICILLIN ON GROWTH-RATE AND HEMOLYSIN ACTIVITY OF GROUP-G STREPTOCOCCUS

The influence of the subminimal inhibitory concentrations (1/3 and 1/4 of the MIC) of penicillin on growth rate and on haemolysin production of a strain of group G Streptococcus was studied. It was shown that 1 /3 of the MIC almost completely inhibited the bacterial growth, but it was not able lo inhibit haemolysin activity in the culture supernate. The generation time of bacteria grown in 1/4 of the MIC was approxima tely twice longer than that of the control culture. In all cultures, t he haemolysin, after being produced (or liberated), reached a peak and decreased to low levels, which could suggest that group G Streptococc us produces some end products of metabolism that are able to inhibit h aemolysin activity.