Isolation of Penicillin-Susceptible Mutants from Penicillinase-Producing Strains of M. pyogenes

Abstract

An agar-plating method is descr. for the specific isolation of non-penicillinase-producing mutants from penicillinase -producing strains of Micrococcus pyogenes. These mutants are quite susceptible to penicillin in contrast to parent wild-type cultures which are resistant. 12 of 13 such strains produced these susceptible mutants. This apparently spontaneous type of mutation occurs with high frequency. No evidence of reversibility of the mutation was obtained.