Novel arrangement of the blaCTX-M-55 gene in an Escherichia coli isolate coproducing 16S rRNA methylase.

A multi-drug resistant Escherichia coli C21 was isolated from a chicken in China. It was shown to be positive for the presence of the bla(TEM-1), bla(CTX-M-55) and rmtB genes by PCR. This strain was examined by phylogenetic grouping, conjugation experiments, plasmid analysis, PCR-based replicon typing and multi-locus sequence typed (MLST). The genetic environment of bla(CTX-M-55) was investigated by PCR mapping. The strain belonged to phylogroup A, ST156. The bla(CTX-M-55) and rmtB genes were found to be present in separate plasmids that belonged to the IncI1 and IncN families, respectively. These antibiotic-resistant plasmids could be transferred to the recipient strain alone or together. A new arrangement of ISEcp1-IS1294-ISEcp1-bla(CTX-M-55)-ORF477, in which the ISEcp1 element was disrupted by another IS1294 element, was identified initially. Conjugative transfer and IS elements found in this study could lead to the rapid dissemination of bla(CTX-M-55) and rmtB among strains of Enterobacteriaceae, which could pose a threat to animal husbandry and public health.