Detection of qnr genes among Escherichia coli isolates of animal origin and complete sequence of the conjugative qnrB19-carrying plasmid pQNR2078.

OBJECTIVES: The aims of this study were to identify qnr genes among quinolone-resistant Escherichia coli isolates from defined disease conditions of companion and farm animals obtained in the BfT-GermVet study, and to gain insight into their localization and the organization of the qnr gene regions.

METHODS: The qnr genes were detected by PCR and confirmed by sequencing. qnr-positive isolates were checked for mutations in DNA gyrase and topoisomerase IV genes by PCR and sequencing of the quinolone resistance-determining regions. Multilocus sequence typing (MLST) was performed for the qnr-positive E. coli isolates. Plasmids harbouring qnr genes were transferred by conjugation into E. coli recipients, subjected to PCR-based replicon typing and plasmid-MLST, and one qnrB19-carrying plasmid was sequenced completely.

RESULTS: Only 2 of 417 E. coli isolates investigated carried qnr genes. Both isolates originated from horses and showed MLST type ST86. They harboured conjugative qnrB19-carrying plasmids, which proved to be indistinguishable by restriction analysis, belonged to incompatibility group IncN, showed plasmid-MLST type ST8 and did not carry other resistance genes. The qnrB19 gene was flanked by copies of the insertion sequence IS26. One of these plasmids, pQNR2078, was sequenced completely and had a size of 42 379 bp. Except for the resistance gene region, plasmid pQNR2078 closely resembled the bla(CTX-M-65)-carrying plasmid pKC396 from E. coli.

CONCLUSIONS: qnr genes were rarely detected among E. coli from animals in the BfT-GermVet study. The qnrB19 gene was detected on conjugative plasmids, with IS26 being likely involved in the mobility of qnrB19.