Figure 1. AmpC β-lactamase–producing Escherichia coli isolates per 1,000 E. coli isolates, Calgary Health Region, 2000–2003. Data are averaged over the 4-year period. The presence of plasmid-mediated AmpC β-lactamase genes was determined using multiplex PCR conditions and primers as described . CMY; isolates positive for chromosomal gene of Citrobacter freundii; non-CMY; isolates negative by multiplex PCR.