Isolation of penicillin-susceptible mutants from penicillinase-producing strains of M. pyogenes.

SummaryTwelve of 13 strains of M. pyogenes which produce penicillinase yielded non-penicillinase-producing mutants which were susceptible to penicillin. This apparent spontaneous type of mutation occurs at a high rate of frequency. Cultivation of a strain of this organism at 45° C significantly increased the number of mutants. No evidence of reversibility of the mutation was obtained.