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Antimicrob. Agents Chemother. doi:10.1128/AAC.01377-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Molecular Epidemiology of CTX-M-producing Escherichia coli in the Calgary Health Region: The Emergence of CTX-M-15-producing isolates

Division of Microbiology, Calgary Laboratory Services; and Department of Pathology & Laboratory Medicine, Medicine, Microbiology and Infectious Diseases, and Critical Care, University of Calgary, Calgary, Alberta, Canada, and the National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba, Canada

^* To whom correspondence should be addressed. Email: johann.pitout{at}cls.ab.ca.

	Abstract

A study was designed to describe the molecular epidemiology of CTX-M-producing Escherichia coli over a 6-year period (2000-2005) in a large well-defined Canadian region with a centralized laboratory system. Molecular characterization was done using isoelectric focusing, PCR, automated sequencing while genetic relatedness was determined with pulsed field gel electrophoresis using XbaI. Of the 552 viable extended-spectrum -lactamase producing E. coli isolated, 354 (64%) were positive for bla_CTX-M genes associated with ISEcp1; 211 produced CTX-M-14, 128 CTX-M-15, 5 CTX-M-2, 4 CTX-M-3, 4 CTX-M-24 and 2 produced CTX-M-27. CTX-M-positive isolates were significantly more resistant to the fluoroquinolones than CTX-M-negative isolates while CTX-M-15-producers were more likely to be resistant to gentamicin and tobramycin. There was a predominance of CTX-M-14 during the first 4 years of the study period with community outbreaks associated with cluster 14A during 2000, 2001 and 2003. A substantial increase of CTX-M-15 occurred during the last 18 months that was due to clusters 15A and 15AR in the hospital and nursing home sectors. Our results demonstrated that the persistence and dissemination of CTX-M genes among E. coli populations in larger geographic healthcare regions is dynamic with the continuous emergence of clonally related CTX-M-15. This study illustrated the importance of molecular surveillance in tracking CTX-M-producing E. coli in the community and investigating their influx into hospitals.

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