Abstract
BackgroundThe association of PMQR and ESBLs in negative-bacteria isolates has been of great concern. The present study was performed to investigate the prevalence of co-transferability of oqxAB and bla CTX-M genes among the 696 Escherichia coli (E. coli) isolates from food-producing animals in South China, and to characterize these plasmids.MethodsThe ESBL-encoding genes (bla CTX-M, bla TEM and bla SHV), and PMQR (qnrA, qnrB, qnrS, qnrC, qnrD, aac(6’)-Ib-cr, qepA, and oqxAB) of these 696 isolates were determined by PCR and sequenced directionally. Conjugation, S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blotting experiments were performed to investigate the co-transferability and location of oqxAB and bla CTX-M. The EcoRI digestion profiles of the plasmids with oqxAB-bla CTX-M were also analyzed. The clonal relatedness was investigated by PFGE.ResultsOf the 696 isolates, 429 harbored at least one PMQR gene, with oqxAB (328) being the most common type; 191 carried bla CTX-M, with bla CTX-M-14 the most common. We observed a significant higher prevalence of bla CTX-M among the oqxAB-positive isolates (38.7%) than that (17.4%) in the oqxAB-negative isolates. Co-transferability of oqxAB and bla CTX-M was found in 18 of the 127 isolates carrying oqxAB-bla CTX-M. These two genes were located on the same plasmid in all the 18 isolates, with floR being on these plasmids in 13 isolates. The co-dissemination of these genes was mainly mediated by F33:A-: B- and HI2 plasmids with highly similar EcoRI digestion profiles. Diverse PFGE patterns indicated the high prevalence of oqxAB was not caused by clonal dissemination.Conclusion bla CTX-M was highly prevalent among the oqxAB-positive isolates. The co-dissemination of oqxAB-bla CTX-M genes in E. coli isolates from food-producing animals is mediated mainly by similar F33:A-: B- and HI2 plasmids. This is the first report of the co-existence of oqxAB, bla CTX-M, and floR on the same plasmids in E. coli.
Highlights
Quinolone resistance was thought to be mediated only by chromosomal mutations, until plasmid-mediated quinolone resistance (PMQR) was described in 1998 [1]
A number of plasmid-mediated quinolone resistance (PMQR) mechanisms have been described: the pentapeptide repeat family Qnr proteins (QnrA, QnrB, QnrS, QnrC, and QnrD) [1,2,3,4,5], AAC(6’)-Ib-cr, an aminoglycoside acetyltransferase that is responsible for reduced susceptibility to ciprofloxacin by modifying ciprofloxacin [6], QepA, an efflux pump belonging to the major facilitator subfamily [7], and OqxAB, a multidrug efflux pump that confers resistance to multiple agents, which has been recently reported to reduce susceptibility to ciprofloxacin and nalidixic acid [8]
ESBL production was detected by the screening method in 206 of the 228 isolates, representing 29.6% of the total 696 E. coli isolates
Summary
Quinolone resistance was thought to be mediated only by chromosomal mutations, until plasmid-mediated quinolone resistance (PMQR) was described in 1998 [1]. There is a paucity of data with regard to the prevalence and characterization of plasmids co-carrying oqxAB-blaCTX-M genes in bacteria, except only one E. coli isolate in our previous report [16]. The present study was performed to investigate the prevalence of co-transferability of oqxAB and blaCTX-M genes among the 696 Escherichia coli (E. coli) isolates from food-producing animals in South China, and to characterize these plasmids. The co-dissemination of oqxAB-blaCTXM genes in E. coli isolates from food-producing animals is mediated mainly by similar F33:A-: B- and HI2 plasmids. This is the first report of the co-existence of oqxAB, blaCTX-M, and floR on the same plasmids in E. coli
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