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

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 beta-lactamase-producing E. coli isolates isolated, 354 (64%) were positive for blaCTX-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.