Molecular Epidemiology of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa in the Calgary Health Region: Emergence of VIM-2-Producing Isolates

A study was designed to describe the molecular epidemiology of carbapenem-resistant (CR)Pseudomonas aeruginosa in a large well-defined geographical region with a centralized laboratory system serving one pediatric and three large adult hospitals (acute care centers I, II, and III). Molecular characterization was done using PCR with sequencing of the integron-associated gene cassettes. Pulsed-field gel electrophoresis (PFGE) using a modified combinedStenotrophomas maltophilia andStreptococcus pneumoniae protocol with SpeI was performed on CRP. aeruginosa strains isolated in the Calgary Health Region during 2002-2006. The majority (96%) of metallo-β-lactamase (MBL)-producing isolates produced VIM-2 with gene cassettesaacC1 andaacA4 , while 4% produced IMP-7 with gene cassettesaacC4 andaacC1 . Eighty-six percent of VIM-2 producers belonged to a cluster (MBLV) that was responsible for nosocomial outbreaks during 2003 (intensive care unit) and 2004 (bone marrow transplant unit) at acute care center I. Environmental isolates from these units also belonged to MBLV. The majority of strains from cluster MBLVR (related to MBLV) were present in acute care center III. Isolates producing IMP-7 belonged to a different cluster (MBLI) and were related to strains described during the 1990s. PFGE of the MBL-negative CR strains showed that 37% belonged to a closely related cluster, NMBL, whose members were predominantly isolated from acute care center II. Our findings suggest that CR and dissemination of MBL clusters amongP. aeruginosa populations in large geographic healthcare regions are dynamic processes that require continuous molecular surveillance.