Unique Features of Plasmid pAC3 and Expression of the Plasmid-Mediated Quinolone Resistance Genes.

A highly fluoroquinolone-resistant isolate of species was isolated from a wastewater treatment plant and found to possess multiple resistance mechanisms, including mutations in and , efflux pumps, and plasmid-mediated quinolone resistance (PMQR) genes. Complete sequencing of the IncU-type plasmid, pAC3, present in the strain revealed a circular plasmid DNA 15,872 bp long containing two PMQR genes [ and ()]. A mobile insertion cassette element containing the gene and a typical miniature inverted-repeat transposable element (MITE) structure was identified in the plasmid. The present study revealed that this MITE sequence appears in other species plasmids and chromosomes. Plasmid pAC3 was introduced into , and its PMQR genes were expressed, resulting in the acquisition of resistance. Proteome analysis of the recipient strain harboring the plasmid revealed that () expression was constitutive and that expression was dependent upon fluoroquinolone stress through regulation by regulator of sigma D (Rsd). To the best of our knowledge, this is the first report to characterize a novel MITE sequence upstream of the PMQR gene within a mobile insertion cassette, as well as the regulation of expression. Our results suggest that this mobile element may play an important role in dissemination. In the present study, plasmid pAC3 isolated from a highly fluoroquinolone-resistant isolate of species was sequenced and found to contain two fluoroquinolone resistance genes, ()- and . Comparative analyses of plasmid pAC3 and other sp. IncU-type plasmids revealed a mobile insertion cassette element with a unique structure containing a gene and a typical miniature inverted-repeat transposable element (MITE) structure. This study also revealed that this MITE sequence appears in other species plasmids and chromosomes. Our results also demonstrate that the fluoroquinolone-dependent expression of is associated with in DH5α harboring plasmid pAC3. Our findings suggest that the mobile element may play an important role in dissemination and that species constitute an important reservoir of fluoroquinolone resistance determinants in the environment.