Nosocomial outbreak of imipenem-resistant Pseudomonas aeruginosa producing VIM-2 metallo-β-lactamase in a kidney transplantation unit

Background: Twenty four non replicate imipenem resistant P. aeruginosa were isolated between January and November 2008, in the kidney transplantation unit of Charles Nicolle Hospital of Tunis (Tunisia). This study was conducted in order to establish epidemiological relationship among them and to identify the enzymatic mechanism involved in imipenem resistance. Methods: Analysis included antimicrobial susceptibility profile, phenotypic (imipenem-EDTA synergy test) and genotypic detection of metallo-beta-lactamase (MBL) (PCR), O-serotyping and pulsed-field gel electrophoresis. Results: All strains showed a high level of resistance to all antimicrobials tested except to colistin. The presence of MBL showed concordance between phenotypic and genotypic methods. Sixteen isolates were identified as VIM-2 MBL-producers and 13 of them were serotype O4 and belonged to a single pulsotype (A). Conclusions: This study describes an outbreak of VIM-2-producing P. aeruginosa in a kidney transplantation unit. Clinical spread of bla(VIM-2) gene is a matter of great concern for carbapenem resistance in Tunisia.