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Antimicrobial Agents and Chemotherapy, July 2009, p. 2846-2851, Vol. 53, No. 7
0066-4804/09/$08.00+0     doi:10.1128/AAC.00247-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Molecular Characteristics of Extended-Spectrum-β-Lactamase-Producing Escherichia coli Isolates Causing Bacteremia in the Calgary Health Region from 2000 to 2007: Emergence of Clone ST131 as a Cause of Community-Acquired Infections {triangledown}

Johann D. D. Pitout,1,2,4* Daniel B. Gregson,1,2,3 Lorraine Campbell,1 and Kevin B. Laupland2,3,5

Division of Microbiology, Calgary Laboratory Services,1 Department of Pathology & Laboratory Medicine,2 Department of Medicine,3 Department of Microbiology and Infectious Diseases,4 Critical Care, University of Calgary, Calgary, Alberta, Canada5

Received 20 February 2009/ Returned for modification 3 April 2009/ Accepted 13 April 2009

A study was designed to characterize extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli isolates causing bacteremia over an 8-year period (2000 to 2007) in a large well-defined geographical region. Molecular characterization was done by using isoelectric focusing; PCR; and sequencing of the blaCTX-M-, blaTEM-, blaOXA-, blaSHV-, and plasmid-mediated quinolone resistance determinants. Genetic relatedness was determined by pulsed-field electrophoresis with XbaI and multilocus sequence typing. A total of 67 patients with incident bloodstream infections were identified, and the majority presented with community-acquired infections involving the urinary and biliary tracts. Of the 67 ESBL-producing E. coli isolates recovered, 60 (90%) were positive for blaCTX-M genes; 32 (48%) produced CTX-M-15, 25 (37%) produced CTX-M-14, 1 (2%) produced CTX-M-24, 1 (2%) produced CTX-M-2, and 1 (2%) produced CTX-M-3, while 2 (3%) produced TEM-52 and 5 (7%) produced SHV-2. Twenty-four (36%) isolates were positive for aac(6')-Ib-cr. The majority of isolates were resistant to ciprofloxacin (60 [90%] isolates) and gentamicin (40 [60%] isolates). The occurrence of ESBL-producing isolates was stable during the first 5 years, but there was a substantial increase from 2005 to 2007, mostly due to clone ST131, which produces CTX-M-15 and CTX-M-14, in blood cultures submitted from the community. Our results illustrated that E. coli clone ST131, which coproduces CTX-M-15, OXA-1, TEM-1, and aac(6')-Ib-cr, has emerged as an important cause of community-onset bacteremia caused by ESBL-producing E. coli isolates; and this is the first study to identify CTX-M-14 in E. coli clone ST131.

* Corresponding author. Mailing address: Calgary Laboratory Services, #9, 3535 Research Road NW, Calgary, Alberta, Canada T2L 2K8. Phone: (403) 770-3309. Fax: (403) 770-3347. E-mail: johann.pitout{at}cls.ab.ca

{triangledown} Published ahead of print on 20 April 2009.

Antimicrobial Agents and Chemotherapy, July 2009, p. 2846-2851, Vol. 53, No. 7
0066-4804/09/$08.00+0     doi:10.1128/AAC.00247-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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