Phenotypic and genotypic detection of efflux-mediated carbapenem resistance in Pseudomonas aeruginosa clinical isolates

Introduction: Pseudomonas aeruginosa is the leading pathogen causing healthcare-associated infections and exhibits high levels of intrinsic resistance, with only a limited number of antibiotics available against it. Against this background, the present study was conducted to identify carbapenem resistance in P. aeruginosa mediated by efflux mechanisms and to assess the in vitro detection of efflux pump activity using efflux pump inhibitors as a diagnostic method.  
Methods: Fifty non-duplicate multidrug-resistant P. aeruginosa isolates from different clinical samples were tested for meropenem (10 µg) susceptibility. All meropenem-resistant strains were tested for efflux-mediated resistance using the Carbonyl Cyanide 3-Chloro Phenylhydrazone (CCCP) phenotypic test and mexE gene detection by conventional PCR.  
Results: All 50 P. aeruginosa isolates were resistant to carbapenem. Of the 12 (24%, 12/50) isolates that exhibited phenotypic resistance by the CCCP method, only seven (14%, 7/50) were mexE gene-positive by conventional PCR.  
Conclusions: These above findings which contribute to multidrug resistance in the local setting, although they are not universally present among all MDR strains, highlight the therapeutic challenge posed by P. aeruginosa and the need for ongoing surveillance and institution-specific antibiotic stewardship.