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 bla CMY-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 bla CMY-2 -like allele, bla CMY-130 . The isolates belonged to distinct pulsotypes, suggesting that the bla CMY-2 gene was not disseminated by clonal expansion of bla CMY-2 -positive strains. The bla CMY-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- Ceu I-PFGE and hybridisation analyses revealed that the bla CMY-2 gene was chromosomally located. A CMY gene-containing region composed of five open reading frames (ORFs) (IS Ecp1 – bla CMY-2 – blc – sugE– Δ encR ) 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 bla CMY-2 genes, including a putative IS 66 -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 bla CMY-2 gene in E. coli . This is the first study reporting a chromosomally encoded bla CMY-2 gene in E. coli . Chromosomally encoded bla CMY-2 might be a source of some plasmid-mediated bla CMY-2 genes and this probably facilitates the spread of cephalosporin-resistant strains.