Mutation of Pseudomonas aeruginosa to piperacillin resistance mediated by beta-lactamase production.

Piperacillin-resistant mutants were detected in each of ten strains of Pseudomonas aeruginosa. The resistance was associated with constitutive production by the strains of high levels of beta-lactamase which was similar in character to the induced chromosomal Id beta-lactamase of the parent strains. This type of mutation to piperacillin-resistance occurred at a low frequency. The beta-lactamase production and piperacillin-resistance were stable on repeated subculture and prolonged storage of the strains.