Induction of Penicillinase by Staphylococci In Vitro and In Vivo

Twenty-eight penicillinase-forming cultures ofStaphylococcus aureusand their penicillinase-negative variants were examined for resistance to benzylpenicillin, methicillin, cephalothin, and cephaloridine. The results supported the view that cephaloridine was more easily destroyed by staphylococcal penicillinase than was cephalothin.In our tube-dilution tests, the minimum inhibitory concentration (M.I.C.) of cephaloridine for methicillin-sensitive cultures was never as high as some of the values reported by other workers who used apparently comparable methods. This was probably due to small differences in technique. The M.I.C. is an unsatisfactory measure of the antibiotic sensitivity of an organism which produces an enzyme which destroys the antibiotic.Methicillin-resistant strains ofStaph. aureushave an intrinsic resistance of `heterogenous' type also to benzylpenicillin, cephalothin, and cephaloridine.

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Induction of Penicillinase by Staphylococci In Vitro and In Vivo

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Biological Reactions of Cephalosporins and Penicillins

Biological Reactions of Cephalosporins and Penicillins

Sensitivity of penicillinase-forming strains ofStaphylococcus aureusand of their penicillinase-negative variants to cephaloridine, cephalothin, methicillin, and benzylpenicillin

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