Characterization of genetic structures of the QepA3 gene in clinical isolates of Enterobacteriaceae.

QepA is one of the genes that confer quinolone resistance in bacteria. The aim of this study was to analyze the genetic structures of plasmids that carry a qepA3, a recently discovered allele of qepA in Enterobacteriaceae clinical isolates. 656 non-redundant Enterobacteriaceae clinical isolates were screened for the qepA3 gene and five isolates were identified to carry the gene. Plasmids were isolated from these isolates and were found to increase antibiotic resistance once the plasmids were transferred to Escherichia coli. These plasmids were subcloned and sequenced to analyze the genetic structures surrounding the qepA3 gene. The results showed that the five plasmids had different genetic structures; two of the qepA3-containning isolates had either the bla CTX-M-14 or bla TEM-12 gene instead of the bla TEM-1 gene. The structures of both pKP3764 and pECL3786 have not been previously described. In comparison with pHPA, there were a number of changes in DNA sequences up- and down-stream of the qepA3 gene. These findings provide better understanding of the genetic variations in qepA3 and would be useful for diagnosis and control of quinolone resistance in clinical settings.