Dissemination of the chromosomally encoded CMY-2 cephalosporinase gene in Escherichia coli isolated from animals

Abstract

In this study, 619 individual Escherichia coli isolates from food-producing and companion animals were analysed to determine the prevalence of the cephalosporinase gene blaCMY-2. In total, 18 CMY-2-producers (2.9%) were detected and exhibited multidrug-resistant phenotypes. One of the CMY-2-producers was found to possess a novel blaCMY-2-like allele, blaCMY-130. The isolates belonged to distinct pulsotypes, suggesting that the blaCMY-2 gene was not disseminated by clonal expansion of blaCMY-2-positive strains. The blaCMY-2 genes were located on IncA/C-, IncHI2- or IncX-type plasmids in 9 (50%) of the 18 E. coli isolates. However, in the other nine isolates I-CeuI-PFGE and hybridisation analyses revealed that the blaCMY-2 gene was chromosomally located. A CMY gene-containing region composed of five open reading frames (ORFs) (ISEcp1–blaCMY-2–blc–sugE–ΔencR) was observed in plasmids from eight strains. A CMY gene-containing region composed of ten ORFs was observed in all of the nine chromosomally encoded blaCMY-2 genes, including a putative IS66-like element inserted in this conserved CMY genetic region in three strains. This conserved CMY genetic region was also found to be inserted into the oriVγ (putative gamma origin), part of the IncX plasmid backbone, by a complete transposition unit flanked by 5-bp DRs (direct repeat sequence) in pS62T. These results demonstrate the high prevalence of the chromosomally encoded blaCMY-2 gene in E. coli. This is the first study reporting a chromosomally encoded blaCMY-2 gene in E. coli. Chromosomally encoded blaCMY-2 might be a source of some plasmid-mediated blaCMY-2 genes and this probably facilitates the spread of cephalosporin-resistant strains.