title: Imipenem-induced resistance to antipseudomonal beta-lactams in Pseudomonas aeruginosa.
abstract: Using clinical isolates of Pseudomonas aeruginosa, we studied the ability of imipenem to antagonize the activity of nine other antipseudomonal beta-lactam antimicrobial agents. Imipenem caused truncation of the zones of inhibition in a disk diffusion test for 91 to 100% of the strains, depending on the beta-lactam tested. Addition of subinhibitory concentrations of imipenem caused a fourfold or greater increase in MICs for 72 of 74 isolates and in 20 to 87% of the tests, again depending on the antibiotic tested. beta-Lactamase assays with both whole-cell suspensions and cell sonicates showed that exposure to subinhibitory concentrations of imipenem resulted in a beta-lactamase production supported the hypothesis that induction of beta-lactamase was responsible for antagonism. In hydrolysis studies with a beta-lactamase extract, most of the antagonized drugs were either not hydrolyzed or only poorly hydrolyzed. We conclude that imipenem induces significantly elevated levels of beta-lactamase in P. aeruginosa. This increase in beta-lactamase is associated with increased resistance of the organism to many other beta-lactam agents.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004058:Diffusion; D004352:Drug Resistance, Microbial; D004355:Drug Stability; D006868:Hydrolysis; D015378:Imipenem; D007525:Isoelectric Focusing; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D013845:Thienamycins / Q000494:pharmacology*; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D013845:Thienamycins; D065093:beta-Lactamase Inhibitors; D015378:Imipenem; D001618:beta-Lactamases