Induction of beta-lactamase in Proteus vulgaris.

Various beta-lactam antibiotics, including monocyclic beta-lactams, induced the beta-lactamase of Proteus vulgaris; when clinical isolates were induced by benzylpenicillin, each strain produced a single beta-lactamase but the activity per milligram dry weight differed from strain to strain. The beta-lactamases of the P. vulgaris strains were heterogeneous with respect to their isoelectric points, but had almost the same specific activities, substrate specificities and Michaelis constants. The kinetics of beta-lactamase formation were investigated in three strains, each with a different beta-lactamase activity. Differential rates of enzyme synthesis and peak activity depended on the concentration of inducer. The plots of the reciprocals of the differential rates versus the reciprocals of the inducer concentrations were linear, and the maximum rate of enzyme synthesis and the concentration of the inducer giving half-maximum induction were determined from this double reciprocal plot. The maximum rates of enzyme synthesis were different in the three strains. The kinetic analysis of beta-lactamase formation revealed that the beta-lactamase activities in a single bacterial species were determined by differences in the rate of enzyme synthesis and not by differences in the properties of the enzyme.