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Antimicrobial Agents and Chemotherapy, January 2005, p. 358-365, Vol. 49, No. 1
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.1.358-365.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Molecular Characterization of Cefoxitin-Resistant Escherichia coli from Canadian Hospitals

Michael R. Mulvey,1* Elizabeth Bryce,2 David A. Boyd,1 Marianna Ofner-Agostini,3 Allison M. Land,1 Andrew E. Simor,4 Shirley Paton,5 and the Canadian Hospital Epidemiology Committee,{dagger} the Canadian Nosocomial Infection Surveillance Program,{ddagger} Health Canada

Nosocomial Infections, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba,1 Division of Nosocomial and Occupational Infections, Centre for Infectious Disease Prevention and Control, Public Health Agency of Canada, Ottawa, Ontario,5 The Vancouver General Hospital, Vancouver, British Columbia,2 The University of Toronto,3 The Department of Microbiology, Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario, Canada4

Received 7 April 2004/ Returned for modification 4 August 2004/ Accepted 11 September 2004

A study designed to gain baseline information on strains of Escherichia coli displaying resistance to cefoxitin in Canada is described. A total of 29,323 E. coli isolates were screened at 12 participating hospital sites as part of an extended-spectrum beta-lactamase surveillance initiative. A total of 411 clinically significant, nonrepeat isolates displaying reduced susceptibilities to the NCCLS-recommended beta-lactams were submitted to a central laboratory over a 1-year period ending on 30 September 2000. Two hundred thirty-two isolates were identified as resistant to cefoxitin. All cefoxitin-resistant strains were subtyped by pulsed-field gel electrophoresis, and of these, 182 strains revealed a unique fingerprint and 1 strain was untypeable. PCR and sequence analysis of the ampC promoter region revealed 51 different promoter or attenuator variants and 14 wild-type promoters. Three promoter regions were interrupted by insertion elements, two contained IS10 elements, and one contained an IS911 variant. PCR and sequence analysis for the detection of acquired AmpC resistance (by the acquisition of ACT-1/MIR-1, CMY-2, or FOX) revealed that 25 strains contained CMY-2, including 7 of the strains found to have wild-type promoters. The considerable genetic variability in both the strain fingerprint and the promoter region suggests that AmpC-type resistance may emerge spontaneously by mutation of sensitive strains rather than by the spread of strains or plasmids in the hospital setting.


* Corresponding author. Mailing address: Nosocomial Infections, National Microbiology Laboratory, 1015 Arlington St., Winnipeg, Manitoba R3E 3R2, Canada. Phone: (204) 789-2133. Fax: (204) 789-5020. E-mail: michael_mulvey{at}hc-sc.gc.ca.

{dagger} Members of the Canadian Hospital Epidemiology Committee are listed in Acknowledgments.

{ddagger} Members of the Canadian Nosocomial Infection Surveillance Program are listed in Acknowledgments.


Antimicrobial Agents and Chemotherapy, January 2005, p. 358-365, Vol. 49, No. 1
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.1.358-365.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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