Induction/inhibition of chromosomal beta-lactamases by beta-lactamase inhibitors.

Many species of gram-negative bacteria produce chromosomal beta-lactamases that can be induced to high-level expression by exposure to beta-lactam antibiotics. Fifty-four strains of Escherichia coli, Enterobacter, Proteus, Citrobacter, and Morganella were examined for beta-lactamase inducibility by clavulanic acid, sulbactam, YTR 830, ampicillin, and cefoxitin. Cefoxitin proved to be the most potent inducer, affecting most of the strains of Enterobacter and Morganella. Clavulanic acid induced 30% of all strains studied. Sulbactam and YTR 830 did not induce measurable levels of beta-lactamases. Inhibition of some chromosomal beta-lactamases by sulbactam and YTR 830 was demonstrated, whereas inhibitory activity by clavulanic acid was found only in Proteus and Citrobacter.