Prevalence of decreased susceptibility to carbapenems among Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii and investigation of carbapenemases

Between March and July 2002, total of 612 clinical isolates of Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii (201 S. marcescens, 228 E. cloacae, and 183 C. freundii) were collected from 13 clinical laboratories in a nationwide distribution. Imipenem and meropenem minimum inhibitory concentrations (MICs) were determined using the agar dilution method according to the National Committee for Clinical Laboratory Standards guidelines. For the isolates with a decreased susceptibility to carbapenems (MICs of ≥2 μg/mL), isoelectric focusing, polymerase chain reaction (PCR) amplification of the carbapenemase genes (blaIMP-1, blaVIM-2, blaSME-1, blaOXA-23, blaOXA-25, blaKPC-1), and sequencing were performed. The prevalence of S. marcescens, E. cloacae, and C. freundii with a decreased susceptibility to imipenem was 17.9% (36/201), 0.4% (1/228), and 0.5% (1/183), respectively, and to meropenem, it was 11.4% (23/201), 0% (0/228), and 0.5% (1/183), respectively. The blaVIM-2 was the only carbapenemase detected, and was found in 0.5% (1/201) of S. marcescens and 0.5% (1/183) of C. freundii isolate.