Induction of drug-destroying enzymes

In this way Staphylococcus aureus becomes resistant to penicillin in the clinic. Penicillin-resistant strains isolated from patients secrete the enzyme p-lactamase ( penicillinase ). This enzyme hydrolyses the drug to penicil-loic acid, which is biologically inert (see Section 12.i). Penicillinase-producing staphylococci are inherently quite sensitive to penicillin. Hence small inocula can be inhibited by low concentrations of the antibiotic. It is, in effect, a race between the speed with which penicillin can kill the bacteria and the speed with which they can produce enough of the enzyme to destroy the penicillin (Knox, 1962). Actually penicillin can be made to induce some strains of Staph, aureus to produce penicillinase. No permanently resistant population of this bacterium has arisen in this way, and the organisms return fairly rapidly to the uninduced susceptible state when the penicillin is withdrawn. Much of the detail of penicillinase-induction was first worked out in Bacillus cereus (Pollock and Ferret, 1951). 

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