[The Prevalence of Metallo-β-Lactamases and Efflux-Mediated Mechanisms in Carbapenem Nonsusceptible Nosocomial Pseudomonas aeruginosa Isolated in Moscow in 2012-2015].

Background: Pseudomonas aeruginosa, the major nosocomial opportunistic pathogen, is an important cause of infectious morbidity and mortality among immunocompromised patients.
Objective: To establish the role of metallo-β-lactamases (MBL) and efflux-mediated mechanisms in confer- ring carbapenem resistance in nosocomial isolates of P. aeruginosa.
Methods: We analyzed carbapenem nonsusceptible nosocomial P. aeruginosa isolates obtained from pediatric and adult patients at three hospitals in Moscow in 2012-2015. Carbapenem susceptibility was assessed using the E-test. In addition, minimal inhibitory concentrations (MICs) of meropenem were tested by the broth microdilution method. The presence of MBL was determined using the ED TA-mediated suppression test. Efflux-dependent resistance was measured using an assay based on MIC modification by an ionophore carbonyl cyanide 3-chlorophenyl hydrazine (CCCP).
Results: A total of 54 carbapenem nonsusceptible P. aeruginosa isolates was examined. The presence of an MBL was detected in 37 (69%) isolates, 29 (54%) isolates had efflux-mediated resistance. In 10 (19%) isolates neither MBL nor efflux activity was found. Five out of 6 isolates (83%) with highly active efflux were MBL-positive. Among isolates with low efflux activity, 74% (17/23) possessed MBL, whereas in isolates with no efflux the rate of MBL-positivity was 60% (15/25).
Conclusion: The prevalence of MBL- and efflux-mediated carbapenem resistance in nosocomial P. aeruginosa is high. Moreover, our results reveal that several resistance mechanisms may combine at the isolate level. These data may contribute to the development of novel strategies in combating carbapenem resistance.