Impact of meropenem exposure on fluoroquinolone and carbapenem resistance in Pseudomonas aeruginosa infection in inpatients in a Japanese university hospital: Insights into oprD mutations and efflux pump overexpression

Objectives: In Pseudomonas aeruginosa isolates, emerging meropenem resistance beyond imipenem resistance has become a problem. In this study, we aimed to investigate the relationship between the in vivo acquisition of antimicrobial resistance in fluoroquinolone- and carbapenem-resistant P. aeruginosa clinical isolates, the underlying molecular mechanisms, and exposure to antimicrobial agents. Methods: Pulsed-field gel electrophoreses were performed to study the molecular relatedness of nine clinical isolates from a Japanese hospital. The minimal inhibitory concentrations of clinically relevant antibiotics were determined. Quantitative PCR was performed to analyze oprD, mexB, mexC, mexE, and mexY expression. DNA sequencing was performed to identify mutations. Results: Eight of nine strains were metallo-β-lactamase (MBL) negative, and one strain was MBL positive. All eight non-MBL-resistant strains harbored mutations in the quinoline-resistance-determining regions (QRDR) of gyrA, gyrB, or parC. Five of the eight non-MBL strains had T83I, two had D87N, and one had both T83I and D87N mutations in gyrA. Of these eight strains, three carrying gyrA mutations had another QRDR mutation in subunits, gyrB or parC, associated with mexY overexpression. Additionally, seven of eight dual fluoroquinolone and carbapenem-resistant isolates carried a premature termination codon within oprD, containing either F170L or L7 shortening. Conclusions: In dual fluoroquinolone- and carbapenem-resistant P. aeruginosa, alterations in the OprD porin and the presence of an active EP are primary resistance mechanisms. Meropenem exposure within the past 59 days may have contributed to the selection of the oprD mutant overexpressing mexB, and meropenem exposure within the past 6 months may have contributed to meropenem resistance.