Prevalence of Ambler class A and D β-lactamases among clinical isolates of Pseudomonas aeruginosa in Korea

Objectives: Recently, resistance to extended-spectrum cephalosporins due to acquired beta-lactamases has been reported in Pseudomonas aeruginosa. The aim of this study was to investigate the prevalence of Ambler class A and D beta-lactamases and their extended-spectrum derivatives and antimicrobial susceptibilities of P. aeruginosa isolated from various parts of Korea. Methods: A total of 252 consecutive, non-duplicate isolates of P. aeruginosa were studied for the presence of class A or D beta-lactamase. Antibiotic susceptibility tests and PCR amplification of genes encoding class A (bla(PSE-1), bla(PER-1), bla(VEB-1), bla(TEM), bla(SHV), bla(CTX-M) and bla(GES-1)) and class D beta-lactamases (bla(OXA-groupI), bla(OXA-groupII) and bla(OXA-groupIII)) were performed. For PCR-positive isolates, isoelectric focusing (IEF) analysis, sequencing and pulsed-field gel electrophoresis (PFGE) were performed. Results: In 64 (25.4%) isolates, structural genes for PSE-1 (6.3%), OXA-10 (13.1%), OXA-4 (4.3%), OXA-30 (2.0%), OXA-2 (2.3%) and OXA-17 (0.4%) were found; their distribution varied between provinces. None harboured bla(PER-1), bla(VEB-1), bla(TEM), bla(SHV), bla(CTX-M) and bla(GES-1). The cross-class resistance rates to other antibiotics was significantly higher in class A and D beta-lactamase producers than in non-producers (P < 0.001 for aminoglycosides, ciprofloxacin and meropenem). Conclusions: OXA-type beta-lactamases are widespread, but their extended-spectrum derivatives are rare among P. aeruginosa in Korea. To our knowledge, this is the first report of OXA-17, an extended-spectrum derivative of OXA-10, outside the Middle East. In addition, combined resistance to ticarcillin and aminoglycosides was a useful indicator for P. aeruginosa producing PSE- or OXA-type beta-lactamases in this study.