Genetic and phenotypic characterization of the bla_CMY gene from escherichia coli and salmonella enterica isolated from food-producing animals, humans, the environment, and retail meat

The bla_CMY-2 family of the ampC β-lactamase genes confer broad-spectrum resistance to β-lactam antimicrobials, including ceftriaxone and ceftiofur, as well as to β-lactamase inhibitors, such as clavulanic acid. Organisms with the bla_CMY-2 phenotype have been recovered from the environment and from retail meat products, posing a potential public health risk. The objectives of this study were to sequence the bla_CMY-2 gene from Escherichia coli and Salmonella enterica from multiple sources that had a reduced susceptibility to ceftriaxone and to determine the effect of observed mutations in the bla_CMY-2 gene on the antimicrobial resistance phenotype (spectrum and minimum inhibitory concentration/susceptibility patterns) of the isolates. The bla_CMY-2 genes from 52 bacterial isolates were sequenced for this study. Sixty-two percent (32/52) were E. coli and 38% (20/52) were S. enterica. Of the 32 E. coli isolates, 30 were found to carry a β-lactamase gene that was 100% homologous to bla_CMY-2. One of the E. coli isolates was found to contain a gene that was 90% homologous to bla_CMY-2. This isolate also had lower minimum inhibitory concentrations to tetracyclines, streptomycin, and the sulfonamide antimicrobials than are commonly expected for isolates containing the bla _CMY-2. Of the 20 genes obtained from Salmonella isolates, 8 (40%) were found to be homologous to bla_CMY-2, with no altered susceptibility phenotypes observed.