Mutational Enzymatic Resistance of Enterobacter Species to Beta-Lactam Antibiotics

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Abstract
Mutants with enhanced β-lactam resistance were selected from strains of Enterobacter cloacae and E. aerogenes by using three antibiotics. High-level β-lactamase-producing mutants had similar degrees of increased resistance, enzyme substrate profiles, and isoelectric (pI) values irrespective of the selective agent. Reverse mutants from a resistant E. cloacae mutant regained the susceptibility pattern originally exhibited by the wild type, or were of enhanced susceptibility, and no longer expressed increased β-lactamase production. β-Lactamases of the mutants were similar in pI values to the wild-type enzyme. The increased resistance of the mutants therefore appeared to be accounted for by increased β-lactamase production.