OBJECTIVES

To evaluate the genetic relatedness and carbapenem resistance mechanisms among carbapenem-non-susceptible Pseudomonas aeruginosa collected during 2009-11 in 14 European and Mediterranean countries.

METHODS

Doripenem-non-susceptible (MIC >2 mg/L) isolates were tested for susceptibility to imipenem, meropenem, doripenem, aztreonam, ceftazidime and cefepime with and without phenyl-arginine-β-naphthylamide (PAβN) (efflux inhibitor) and/or cloxacillin (AmpC inhibitor). Carbapenemase screening was performed by PCR and sequencing. Expression of chromosomal ampC, mexA, mexC, mexE and mexX was determined by quantitative real-time PCR using P. aeruginosa PAO1 or a group of susceptible isolates as baseline. Clonality was evaluated by PFGE and multilocus sequence typing.

RESULTS

Among 529 (25.6% overall) carbapenem-non-susceptible P. aeruginosa, 106 were positive for metallo-β-lactamase (MβL) genes encoding VIM-2 (76 strains), VIM-4 (14), VIM-1 (7) and VIM-5 (5). IMP-15 and three new MβLs (IMP-33, VIM-36 and VIM-37) were detected in one strain each. An increasing prevalence of MβL producers was noted in 2011 (30.6%) compared with previous years (13.4% and 12.3% in 2009 and 2010, respectively). Isolates displayed high genetic diversity, with 401 unique profiles detected. CC235 and ST111 were detected among MβL-producing clusters. The PAβN/cloxacillin effect ranged from 90.0% to 56.5%/from 1.3% to 21.2%. OprD decrease/loss was the most prevalent intrinsic mechanism and was detected among 94.9% of the P. aeruginosa, followed by AmpC (44.4%) and MexAB-OprM (20.1%). When using the susceptible group of isolates as baseline, MexAB-OprM became as prevalent as OprD decrease/loss.

CONCLUSIONS

Increasing MβL prevalence is worrisome in various European countries; however, intrinsic resistance mechanisms in a highly genetically diverse population of carbapenem-non-susceptible P. aeruginosa are probably a matter for greater concern in these countries.