High-level resistance to meropenem in clinical isolates of Pseudomonas aeruginosa in the absence of carbapenemases: role of active efflux and porin alterations

作者：Chalhoub Hussein; Saenz Yolanda; Rodriguez Villalobos Hector; Denis Olivier; Kahl Barbara C; Tulkens Paul M; Van Bambeke Francoise

来源：International Journal of Antimicrobial Agents, 2016, 48(6): 740-743.

DOI：10.1016/j.ijantimicag.2016.09.012

• Cystic fibrosis
• Hospital-acquired pneumonia
• MexAB-OprM
• Carbapenemase
• OprD

High-level carbapenem resistance is worryingly increasing in clinical isolates and is often attributed to carbapenemase expression. This study aimed to determine the mechanisms leading to high-level meropenem resistance in six carbapenemase-negative Pseudomonas aeruginosa isolated from cystic fibrosis (CF) patients and seven carbapenemase-positive isolates from patients suffering from hospital-acquired pneumonia (HAP). MICs were determined in the absence or presence of L-arginine or glycine-glutamate as competitive substrates for OprD (OccD1) or OpdP (OccD3), respectively, or the efflux pump inhibitor Phe-Arg beta-naphthylamide (PA beta N). beta-Lactamases were screened by phenotypic tests and/or PCR. The oprD gene and its promoter were sequenced; protein expression was evidenced by SDS-PAGE. mexA, mexX, mexC and mexE transcripts were evaluated by real-time and semiquantitative PCR. Meropenem/ imipenem MICs were 64-128/16-32 mg/L and 128/128-256 mg/L in CF and HAP isolates, respectively; PA beta N reduced meropenem MICs to 4-16 mg/L only and specifically in CF isolates; porin competitors had no effect on MICs. All isolates showed an increase in transcription levels of mexA, mexX and/or mexC and mutations in oprD leading to production of truncated proteins. AmpC-type cephalosporinases were overexpressed in CF isolates and VIM-2 was expressed in HAP isolates. Antibiotic exclusion from bacteria by concomitant efflux and reduced uptake is sufficient to confer high-level resistance to meropenem in isolates overexpressing AmpC-type cephalosporinases. As efflux is preponderant in these isolates, it confers a paradoxical phenotype where meropenem is less active than imipenem. Concomitant susceptibility testing of both carbapenems and rapid elucidation of the most probable resistance mechanisms is thus warranted.

• 出版日期2016-12