Background: The incidence of infections with imipenem-resistant Acinetobacter baumannii (IRAB) and Pseudomonas aeruginosa (IRPA) is increasing worldwide, and recent molecular studies indicate that the prevalence of carbapenemases is increasing in various parts of the world. However, few long-term longitudinal studies have assessed the prevalence of IRAB- and IRPA-derived carbapenemases and integrases in a hospital setting in Korea.

Methods: The carbapenemase genes (bla_OXA-23, bla_OXA-24, bla_OXA-58, bla_IMP-1, bla_VIM-2, bla_SIM-1, bla_SPM-1) and integrase genes (intI1, intI2, intI3) produced by 46 IRAB strains and 51 IRPA strains collected at Chosun University Hospital between 2003 and 2006 were determined by PCR.

Results: The IRAB strains produced class 1 integrases more often than did the IRPA strains. However, the incidence increased steadily in both strains, reaching 100% in 2006. Carbapenemases of bla_IMP-1 and bla_VIM-2 types were found in 57% and 64% of the IRAB strains, respectively, in 2003. However, only one strain with bla_VIM-2 was found in 2004 and another one with bla_IMP-1 in 2005. The prevalence of carbapenemases was very low in the IRPA strains, just one strain with bla_VIM-2 in 2005 and another one with bla_oxa-23 in 2006. No other types of carbapenemase genes were detected in both strains. Rep-PCR of IRAB strains in 2003 showed different patterns.

Conclusion: The incidence of carbapenemase varied by year but was generally low, except in 2003. The prevalence of class 1 integrases was consistently high and increased every year. The reason for the high prevalence of carbapenemases in 2003 is still unknown, but we assumed that it was not from the spread of a clone containing either bla_IMP-1 or bla_VIM-2 because the strains exhibited different rep-PCR patterns. (Korean J Clin Microbiol 2007;10:128-134)