Production of Extracellular Penicillin-Inactivating Substances Associated with Penicillin Resistance in Staphylococcus aureus.

Abstract

A potent penicillin-inactivating substance is produced by penicillin-resistant S. aureus but not by penicillin-sensitive strains. All organisms which grew readily in 5 or more units penicillin/ml. of culture medium were strong producers of the substance; those which were inhibited by penicillin in the range of 5-0.1 units/ml. produced the substance either weakly or in some cases, not at all; in no cases did. the organisms requiring < 0.1 units per ml. for complete inhibition produce the substance. The substance is soluble, diffuses readily into solid medium (as demonstrated by the inactivation of penicillin contained in agar plates), and is present in the supernatants of liquid broth cultures. The variation of susceptibility to penicillin among various strains of S. aureus appears to be associated with a difference in the production of this extracellular penicillin-inactivating substance which, presumably, is penicillinase.