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INDUCTION OF STAPHYLOCOCCAL PENICILLINASE BY BENZYLPENICILLIN: EFFECT OF pH, CONCENTRATION OF FERROUS ION AND INDUCER, AND DURATION OF EXPOSURE OF CELLS TO INDUCER

Department of Microbiology, Michael Reese Hospital and Medical Center, Chicago, Illinois

ABSTRACT

LEITNER, FELIX (Michael Reese Hospital and Medical Center, Chicago, Ill.), HELEN M. SWEENEY, T. F. MARTIN, AND SIDNEY COHEN. Induction of staphylococcal penicillinase by benzylpenicillin: effect of pH, concentration of ferrous ion and inducer, and duration of exposure of cells to inducer. J. Bacteriol. 86:717–727. 1963.—The kinetics of induction of penicillinase by benzylpenicillin in exponentially multiplying Staphylococcus aureus strain 55-C-1 were shown to vary with the pH. At pH 7.3 in the absence of free inducer, the rate of increase of penicillinase activity rapidly declined and came to a halt. At pH 5.4 to 5.5 and in the presence of optimal concentrations of Fe⁺⁺, the penicillinase activity of the induced culture increased linearly with time for 2.5 or more generations, but the rate of increase usually declined eventually. Evidence was advanced to support the concept that the acidic pH and optimal Fe⁺⁺ concentration maintain the induced formation of enzyme. The induced increase in penicillinase activity appeared 3 to 4 min after the addition of benzylpenicillin. The degree of induction of penicillinase varied with the duration of exposure of the staphylococci to the inducer and with the concentration of inducer. Maximal induction under our conditions was attained by exposure for 15 min to benzyl-penicillin at an initial concentration between 0.6 and 2 units/ml.