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Molecular Epidemiology of CTX-M-Producing Escherichia coli in the Calgary Health Region: Emergence of CTX-M-15-Producing Isolates

Division of Microbiology, Calgary Laboratory Services,¹ Departments of Pathology & Laboratory Medicine,² Medicine,³ Microbiology and Infectious Diseases,⁴ Critical Care, University of Calgary, Calgary, Alberta, Canada,⁵ National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba, Canada⁶

Received 3 November 2006/ Returned for modification 9 January 2007/ Accepted 19 January 2007

A study was designed to describe the molecular epidemiology of CTX-M-producing Escherichia coli over a 6-year period (2000 to 2005) in a large well-defined Canadian region with a centralized laboratory system. Molecular characterization was done by isoelectric focusing, PCR, and automated sequencing, while genetic relatedness was determined by pulsed-field gel electrophoresis with XbaI. Of the 552 viable extended-spectrum ß-lactamase-producing E. coli isolates isolated, 354 (64%) were positive for bla_CTX-M genes associated with ISEcp1; 211 produced CTX-M-14, 128 produced CTX-M-15, 5 produced CTX-M-2, 4 produced CTX-M-3, 4 produced 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 in CTX-M-15 producers occurred during the last 18 months and was due to clusters 15A and 15AR (where AR indicates related to A) in the hospital and nursing home sectors. Our results demonstrate that the persistence and dissemination of CTX-M genes among E. coli populations in larger geographic health care regions is dynamic, with the continuous emergence of clonally related CTX-M-15. This study illustrates the importance of molecular surveillance in tracking CTX-M-producing E. coli strains in the community and investigating their influx into hospitals.

Published ahead of print on 5 February 2007.

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