Molecular epidemiology and mechanisms of carbapenem resistance in Pseudomonas aeruginosa isolates from Chinese hospitals

We investigated the molecular epidemiology and carbapenem resistance mechanisms of 258 non-duplicate carbapenem-resistant clinical isolates of Pseudomonas aeruginosa collected from 2006 to 2007 at 28 hospitals in China. Up to 88% of the carbapenem-resistant isolates were multidrug-resistant. Pulsed-field gel electrophoresis (PFGE) revealed that levels of intrahospital and interhospital dissemination of clones were low. To assess the mechanisms leading to resistance, all 258 carbapenem-resistant isolates were analysed for expression of the chromosomal β-lactamase (AmpC), the porin important for entry of carbapenems (OprD) and an efflux system (MexAB-OprM) known to extrude some β-lactams. Carbapenem resistance was driven mainly by mutational inactivation of OprD, accompanied or not by hyperexpression of AmpC or MexAB-OprM. Metallo-β-lactamase genes were detected in 22 carbapenem-resistant isolates in China, belonging to eight pulsotypes. The blaOXA-50 gene was detected among all of the carbapenem-resistant isolates, whereas the blaGES-5 gene was detected in only one carbapenem-resistant isolate.