Fluoroquinolone Enhances the Mutation Frequency for Meropenem-Selected Carbapenem Resistance in Pseudomonas aeruginosa , but Use of the High-Potency Drug Doripenem Inhibits Mutant Formation

The mutation frequency for carbapenem resistance in Pseudomonas aeruginosa strains that were selected with carbapenems was enhanced in the presence of subinhibitory concentrations of fluoroquinolones. The mutants showed either a loss of OprD activity or increased mexAB-oprM expression. The highest mutant isolation frequency was obtained by selection with meropenem, while doripenem inhibited mutant growth.