INCREASED STAPHYLOCOCCAL PENICILLINASE ACTIVITY ACCOMPANYING PENICILLIN TREATMENT OF EXPERIMENTALLY INFECTED MICE

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Abstract
Staphylococci separated by dif-ferential centrifugation from the kidneys of mice infected intravenously with 0.1 ml of a broth culture of a penicillin-resistant Staphylococcus aureus strain possessed the same basal (constitutive) level of penicillinase as cells of the infecting strain grown in vitro. When the mice were treated for 36 hours prior to sacrifice with procaine penicillin G, the staphylococci separated from their kidneys possessed 9 times the basal penicillinase level. No evidence could be obtained that the higher penicillinase activity of the staphylococci from treated mice is the result of selection and it was concluded that staphylococcal penicillinase is probably an inducible enzyme in vivo as well as in vitro.