Background: Spread of imipenem-resistant Pseudomonas aeruginosa isolates is an important clinical threat. The aim of this study is to survey the prevalence of carbapenem-resistant P. aeruginosa isolates in a university hospital, Busan, Korea, and to determine the mechanisms of the resistance.

Methods: P. aeruginosa isolates from the patients in Kosin University Gospel Hospital were collected during the period of June through September, 2004. Antimicrobial susceptibilities were tested by the disk diffusion method, and production of carbapenemase and metallo-β-lactamase was determined by the modified Hodge and EDTA-disk synergy tests, respectively. MICs were determined by the agar dilution method, and pIs of β-lactamases were determined by the isoelectric focusing. Genotypes of carbapenemases were determined by direct sequencing of amplified products.

Results: A total of 77 clinical isolates of P. aeruginosa were collected. Twenty-two (55.0%) and 15 (37.5%) isolates showed positive results in the modified Hodge and EDTA-disk synergy tests, respectively. Searches for bla_OXA-23 and bla_IMP-1 genes showed positive results in 15 and 12 isolates, respectively. MIC ranges of imipenem and meropenem to OXA-23-producing isolates were 8-16 ㎍/mL and 2-32 ㎍/mL, respectively, and those to IMP-1-producing isolates were 2-≥256 ㎍/mL and 2128 ㎍/mL, respectively.

Conclusion: Production of OXA-23 or IMP-1 is the most prevalent mechanism of imipenemresistance in P. aeruginosa isolates in a university hospital, Busan, Korea. Periodical surveys are necessary to monitor the spreading of imipenem-resistant isolates and emerging new mechanisms of imipenem-resistance. (Korean J Clin Microbiol 2005;8(1):26-33)