Characterization of clinical extensively drug-resistant Pseudomonas aeruginosa in the Hunan province of China.

BACKGROUND: Pseudomonas aeruginosa strains that are classed as extensively drug resistant (XDR-PA) are resistant to all antibiotics except for one or two classes and are frequently the cause of hard-to-treat infections worldwide. Our study aimed to characterize clinical XDR-PA isolates recovered during 2011-2012 at nine hospitals in the Hunan province of China.

METHODS: Thirty-seven non-repetitive XDR-PA strains from 37 patients were investigated for genes encoding antimicrobial resistance determinants, efflux pumps, outer membrane proteins, and movable genetic elements using polymerase chain reaction (PCR). The expression of genes encoding the efflux pump component MexA and the outer membrane protein OprD was measured using real-time PCR. In addition, clonal relatedness of these XDR-PA isolates was analyzed by pulsed-field gel electrophoresis (PFGE).

RESULTS: Various genes encoding antimicrobial resistance determinants were found in all isolates. In particular, the bla TEM-1, bla CARB, armA, bla IMP-4, bla VIM-2, and rmtB, were found in 100, 37.8, 22, 22, 19 and 5 % of the isolates, respectively. Remarkably, two isolates coharbored bla IMP-4, bla VIM-2, and armA. In all 37 antibiotic-resistant strains, the relative expression of oprD was decreased while mexA was increased compared to the expression of these genes in antibiotic-susceptible P. aeruginosa strains. All of the XDR-PA isolates harbored class I integrons as well as multiple other mobile genetic elements, such as tnpU, tnp513, tnpA (Tn21), and merA. A high genotypic diversity among the strains was detected by PFGE.

CONCLUSIONS: Multiple antibiotic-resistance mechanisms contributed to the drug resistance of the XDR-PA isolates investigated in this study. Thus, the XDR-PA isolates in this area were not clonally related. Instead, multiple types of movable genetic elements were coharbored within each XDR-PA isolate, which may have aided the rapid development of these XDR-PA strains. This is the first report of XDR-PA strains that coharbor bla IMP-4, bla VIM-2, and armA.