Prevalence and Characterization of Extended-Spectrum Beta-Lactamase-Producing Enterobacteriaceae Isolated in Canadian Hospitals: Results from CANWARD 2007

OBJECTIVE: The purpose of the present study was to determine the prevalenceand molecular epidemiology of extended-spectrum beta-lactamase(ESBL)-producing Enterobacteriaceae identified from Canadian hospitalsin 2007.METHODS: Clinically significant isolates were collected as part of theCanadian Ward Surveillance Study (CANWARD 2007) from January toDecember 2007, inclusive, from 12 sentinel hospital centres across Canada.Minimum inhibitory concentrations were determined by broth microdilution,and putative ESBL isolates were confirmed by the Clinical andLaboratory Standards Institute disk diffusion method. Polymerase chainreaction and DNA sequencing were used to detect blaSHV, blaTEM, blaCTX-Mand blaOXA-like genes. Strains were typed using pulsed-field gel electrophoresis.RESULTS: A total of 3.4% and 1.6% of Escherichia coli and Klebsiellapneumoniae, respectively, were identified as ESBL producers. Resistance tofluoroquinolones, doxycycline, trimethoprim/sulfamethoxazole and gentamicinoccurred in 92.5% and 71.4%, 75.5% and 71.4%, 67.9% and57.1%, and 58.5% and 57.1% of ESBL-producing E coli and K pneumoniae,respectively. A total of 90.6% and 71.4% of ESBL-producing E coli andK pneumoniae were identified as multidrug resistant. The CTX-M type wasthe predominant ESBL, with CTX-M-15 as the predominant genotype. Atotal of 81.7% ESBL-producers carried several beta-lactamase genes.Pulsed-field gel electrophoresis revealed that the majority of ESBL producerswere not genetically related (less than 80% homology). Similar patientdemographics were observed among both ESBL-producing E coli and Kpneumoniae.CONCLUSION: CTX-M has become the most common enzyme amongboth ESBL-producing E coli and K pneumoniae. The spread of ESBLproducingbacteria across Canada is polyclonal and is not due to the clonalspread of a single strain