Different penicillin sensitivities between capsulated strains of Staphylococcus aureus and their non-capsulated variants.

Four capsulated strains of Staphylococcus aureus were penicillin sensitive and qualitatively negative for penicillinase; however, their non-capsulated variants were all resistant to penicillin and positive for penicillinase. With a capsulated strain, remarkably low penicillinase was detected within cells when the organisms were broken by sonic oscillation and the majority of the remarkably higher penicillinase activity in its non-capsulated variant was found in the cell surface fraction. When the capsulated strain was cultured in plain brain heart infusion broth at 43 degrees C for 72 h, the majority of the organisms did not produce capsules and significantly higher penicillinase activity was found in the culture supernatant.