Characteristics of Acquired β-lactamase Gene in Clinical Isolates of Multidrug-resistantPseudomonas aeruginosa

Background: Recently, there have been reports of infections with multidrug-resistant Pseudomonas aeruginosa. To determine the mechanism of the resistance, we investigated the prevalence of Ambler class A and D β-lactamases, their extended-spectrum derivatives, and class B and D carbapenemase in multidrug-resistant P. aeruginosa isolates. Methods: During the period of March 2006 to May 2007, clinical isolates of multidrug-resistant P. aeruginosa were collected from patients in Chungnam National University Hospital, Daejeon, Korea. Inhibitor-potentiated disk diffusion tests were used for the screening of metallo-β-lactamase (MBL) production. PCR and DNA sequencing were conducted for the detection of β-lactamase genes. We also employed the enterobacterial repetitive intergenic consensus (ERIC)PCR method for an epidemiologic study. Results: A total of 37 consecutive, non-duplicate, multidrug-resistant P. aeruginosa were isolated. Twentynine of 37 isolates harbored blaOXA-10 (56.8%), blaOXA-2 (18.9%), and blaOXA-1 (5.4%). Only one isolate produced IMP-1, and it also harbored blaOXA-1. None harbored Ambler class A β-lactamase or class D carbapenemase. The strains producing OXA type β-lactamases showed a significantly higher resistance to aminoglycoside compared to non-producers. The ERIC-PCR pattern of the 19 OXA-10 producing strains indicated that the isolates were closely related in terms of clonality. Conclusion: OXA type β-lactamases are the most prevalent among the acquired β-lactamases produced by multidrug-resistant P. aeruginosa isolated at a university hospital in Chungcheong Province. Besides β-lactam antibiotics, the strains harboring OXA type β-lactamase showed a significantly higher resistance to aminoglycoside and qunolone. (Korean J Clin Microbiol 2008;11:98-106)