Prevalence of extended-spectrum β-lactamase-producing Enterobacteriaceae with focus on the molecular characterization of ESBL- and AmpC β-lactamase- producing Escherichia coli isolated in Canadian hospitals from 2005-2009

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Simner, Patricia Jeanne
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The spread of resistance to the cephalosporins in the Enterobacteriaceae and more specifically within E. coli is a continuing cause of public health concern, with such resistance increasingly seen in community- and nosocomial-acquired infections. Extended-spectrum ß-lactamase (ESBL) and AmpC ß-lactamase (AmpC) enzymes cause most cephalosporin resistance in E. coli by hydrolysis of the antimicrobial and continue to jeopardize patient outcome. The purpose of this thesis was to determine the prevalence of ESBL-producing Enterobacteriaceae and to molecularly characterize ESBL and AmpC producers found to be associated with the increasing cephalosporin resistance among E. coli within Canadian hospitals from 2005 to 2009. Isolates were collected as part of the Canadian Intensive Care Unit and Canadian Ward surveillance studies. ESBL and AmpC producers were molecularly characterized for resistance genes, virulence factors and phylogenetic groups. All strains were typed using PFGE and ESBL-producing E. coli were further typed by MLST. Plasmids bearing the ESBL and AmpC genes were characterized by BglII RFLP analysis and a multiplex PCR for replicon typing. ESBL-producing E. coli and K. pneumoniae and AmpC-producing E. coli were found to be firmly established in Canadian hospitals; whereas, ESBL-producing K. oxytoca and P. mirabilis have yet to emerge. Increasing resistance to several unrelated antimicrobials leading to multi-drug resistance among these pathogens is concerning. The successful dissemination of ESBL-producing E. coli in Canada occurs through a diversity of different mechanisms and does not correspond to a single ESBL determinant, or a single clone, or a single plasmid but rather through the combination of clonal spread of virulent strains and the acquisition of diverse ESBL-bearing plasmids. However, the predominance of CTX-M-15-producing E. coli in this study was mainly due to the virulent ST131 clone and the diverse IncFII plasmids bearing the blaCTX-M-15 gene. Whereas, horizontal transfer of genetically similar IncI1, IncA/C and IncK/B plasmids bearing blaCMY-2 and the clonal spread of virulent strains, including ST131 with ampC promoter/attenuator mutations, appears to be playing a role in the spread of AmpC-producing E. coli isolates in Canadian hospitals. The increasing prevalence of these multi-drug resistant pathogens in Canadian hospitals demonstrates the need for increased surveillance and understanding of these emerging pathogens. The continued surveillance will help guide proper infection control procedures and identify optimal treatment of these clinically important pathogens in Canadian hospitals.
Beta-Lactamases, Escherichia coli, Canada, Enterobacteriaceae
Simner PJ, GG Zhanel, J Pitout, F Tailor, M McCrcken, MR Mulvey, PRS Lagacé-Wiens, HJ Adam, the Canadian Antimicrobial Resistance Alliance (CARA) and DJ Hoban. 2011. Prevalence and Characterization of Extended-Spectrum ß-Lactamase-and AmpC ß-Lactamase-Producing Escherichia coli: Results of the CANWARD 2007-2009 Study. Diagn Microbiol Infect Dis. In press.
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