Abstract
BackgroundIt has been demonstrated that swine waste is an important reservoir for resistant genes. Moreover, the bacteria carrying resistant genes and originating from swine feces and wastewater could spread to the external environment. Fluoroquinolones (FQs) are widely used in livestock and poultry for the treatment of bacterial infection. However, resistance to FQs has increased markedly.ResultsIn this study, swine feces and wastewater were sampled from 21 swine farms of seven provinces in China to investigate the prevalence of FQ resistance, including plasmid-mediated fluoroquinolone resistance (PMQR) genes and the occurrence of target mutations. All isolates showed moderate rate of resistance to norfloxacin (43.0%), ciprofloxacin (47.6%), ofloxacin (47.0%) and levofloxacin (38.8%). The percentage of strains resistant to the four FQs antimicrobials was positively correlated with the danofloxacin (DANO) MIC. Among the 74 FQ-resistant isolates, 39 (52.70%) had mutations in gyrA (S83L and D87 to N, Y, G, or H), 21 (28.38%) had mutations in parC (S80I and E84K), 2 (2.70%) had mutations in parE (I355T and L416F), 26 (35.14%) had mutations in marR (D67N and G103S), 1 (1.35%) had mutations in acrR (V29G). While, no mutation was found in gyrB. There were 7 (9.46%) strains carried the qnrS gene, 29 (39.19%) strains carried the oqxAB gene, and 9 (12.16%) strains carried the aac (6′)-Ib-cr gene. In addition, the conjugation assays showed that qnrS, oqxAB and aac (6′)-Ib-cr could be successfully transferred to E. coli J53 from 4 (57.1%), 20 (69.0%) and 5 (55.6%) donor strains, respectively. There were no qnrA, qnrB, qnrC, qnrD and qepA genes detected.ConclusionThe present study showed that DANO-resistant E. coli strains isolated from swine farms had significant cross-resistance to other four FQs antimicrobials. Further study revealed that the resistance mechanisms of swine-derived E. coli to FQs may be attributable to the occurrence of chromosomal mutations (gyrA, parC, parE, marR and acrR genes double-site or single-site mutation) and the presence of PMQR genes (qnrS, oqxAB and aac (6′)-Ib-cr). To the best of our knowledge, one novel mutation marR-D67N was found to be associated with FQ resistance, two mutations parE-L416F and acrR-V29G have never been reported in China.
Highlights
It has been demonstrated that swine waste is an important reservoir for resistant genes
From July 2014 to March 2017, a total of 1222 E. coli were recovered from swine feces (1000) and wastewater (222)
A total of 74 E. coli strains resistant to the four FQs antimicrobials were selected for further study to determine the prevalence of plasmid-mediated fluoroquinolone resistance (PMQR) genes and the occurrence of target mutations in Fluoroquinolone resistance determining region (QRDR)
Summary
It has been demonstrated that swine waste is an important reservoir for resistant genes. Due to the restricted choice of antimicrobials as well as the dearth of novel classes of antimicrobials emergence, the infections caused by multidrug-resistant bacteria (MRB) are often accompanied by high morbidity and mortality [2]. It is generally accepted that the emergence and prevalence of MRB is associated with the widespread, unreasonable, and increasing use of antimicrobials. This could raise a potential risk for the selection of bacteria to become resistant and promote the dissemination of antimicrobial-resistant bacteria (ARB) and resistance genes [3]. Animals are regarded as an important reservoir of resistance genes or ARB which could cause bacterial infection in humans [4]. The level of resistance in commensal E. coli is regarded as a good indicator for potential selection pressure exerted by regular use of antimicrobials and for investigation of resistance problems in pathogenic bacteria [3, 7]
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