Prevalence of Metallo-β-lactamases in Imipenem-non-susceptible Pseudomonas aeruginosa and Acinetobacter baumannii

Background: Metallo-β-lactamases (MBLs) have been reported in gram negative bacilli and are becoming increasingly important clinically because the enzymes hydrolyse almost all β-lactams, including carbapenems. Thus, the present study was conducted to determine the prevalence of MBL types in imipenem-nonsusceptible Pseudomonas aeruginosa and Acinetobacter baumannii isolated from a tertiary teaching hospital. Methods: Imipenem-nonsusceptible strains, 128 P. aeruginosa and 93 A. baumannii, were collected from clinical specimens. Identification and susceptibility tests were determined by Vitek GNI and GNS cards. MBL production was determined by modified Hodge test and imipenem-EDTA synergy test. Multiplex PCR amplification of MBL genes including blaIMP-1, blaVIM-1 and blaVIM-2 were performed. Results: Thirty-one P. aeruginosa (24.2%) isolates and 3 A. baumannii (3.2%) were found to be MBL producers. In P. aeruginosa, 20 (15.6%) and 11 (8.6%) isolates were positive for blaIMP-1 and blaVIM-2, respectively whereas 1 (1.0%) and 2 (2.2%) isolates in A. baumannii, respectively. Conclusion: IMP-1 is more prevalent MBL type than VIM-2 among imipenem-nonsusceptible P. aeruginosa unlike in other studies. Larger numbers of isolates and sequential studies are strongly recommended for the useful evaluation and monitoring of MBL production in the hospital setting to infection-control. (Korean J Clin Microbiol 2010;13:169-172)