Prevalence and characterization of extended-spectrum β-lactamase- and AmpC β-lactamase-producing Escherichia coli: results of the CANWARD 2007-2009 study.

The national prevalence of extended-spectrum β-lactamase (ESBL)-producing (2007: 3.4%, 2008: 4.9%, 2009: 4.3%) and AmpC β-lactamase (AmpC)-producing (2007: 0.8%, 2008: 3.2%, 2009: 2.7%) Escherichia coli in Canadian hospitals have fluctuated from 2007 to 2009. Rates of co-resistance to non-lactam agents are elevated, and multidrug-resistant (MDR) phenotype were observed among E. coli strains producing ESBLs (83.3% MDR) and AmpCs (31.0%). The majority (>98%) of isolates remained susceptible to colistin, tigecycline, amikacin, and the carbapenems. CMY-2 encoding gene was detected in 52.9% of AmpC-producing strains, while bla(CTX-M-15) (65.2%) was the predominant ESBL genotype. A total of 50.3% of ESBL-producing E. coli and 21.4% of AmpC producers belonged to the ST131 clone. In conclusion, ESBL- and AmpC-producing E. coli are established in Canadian hospitals; and although the prevalence rates of these isolates remain low, they are often MDR and associated with the ST131 clone.