Background: The genes of metallo-β-lactamase (MBL), a powerful carbapenemase, are carried as a part of the mobile gene cassettes inserted into integrons playing an important role in rapid dissemination of antibiotic resistance genes among bacterial isolates. In this study, we investigated carbapenemase genes and class 1 integrons integrated into the gene cassettes in imipenem-non susceptible P. aeruginosa.

Methods: From July 2006 to March 2008, 81 consecutive, non-duplicate, imipenem-non susceptible P. aeruginosa were isolated at Chungnam National University Hospital in Chungcheong province of Korea. The modified Hodge and double disk synergy tests were conducted for the screening of carbapenemase and MBL production, respectively, and PCR and DNA sequencing were performed for the detection of carbapenemase genes and class 1 integron gene cassettes. We also employed the repetitive element sequence-based (Rep)-PCR method for an epidemiologic study.

Results: MBLs were detected in 13.6% (11/81) of imipenem-non susceptible P. aeruginosa. Ten isolates were found to carry bla_IMP-1, whereas 1 isolate was found to carry a bla_VIM-2. All of the IMP-1-producing strains harbored 4.0 kb class 1 integron containing chloramphenicol, aminoglycoside, and β-lactam- resistant genes. However, bla_IMP-1 was not detected at class 1 integron. A 2.5 kb class 1 integron harboring bla_VIM-2 was detected in a VIIM-2- producing strain. One identical pattern was observed in ten IMP-1 producing strains.

Conclusion: IMP-1 producing P. aeruginosa strains are currently distributed throughout Chungcheong province of Korea. In particular, all of the strains harbored class 1 integrons containing variant antibiotic resistance gene cassettes. (Korean J Clin Microbiol 2009;12:17-23)