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

Abstract

The bla(CMY-2) family of the ampC beta-lactamase genes confer broad-spectrum resistance to beta-lactam antimicrobials, including ceftriaxone and ceftiofur, as well as to beta-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 beta-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.