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Background <p>Florfenicol is a critical antibiotic used in cattle to manage respiratory infections, while azithromycin is recommended for treating early-stage Shiga toxin-producing <i>Escherichia coli</i> (STEC) infections. This study focused on examining the co-resistance and mechanisms of co-dissemination of resistance to florfenicol and azithromycin in 367 non-O157 STEC strains isolated from cattle in Xinjiang between 2015 and 2023.</p> Results <p>Among these isolates, 16.3% showed resistance, with drug resistance rates ranging from 5.4 to 10.6% for tetracycline, ampicillin, cefotaxime, streptomycin, sulfamethoxazole, florfenicol, aztreonam, azithromycin, gentamicin, ceftazidime, and piperacillin. Resistance to cefepime, ampicillin-sulbactam, amikacin, amoxicillin-clavulanic acid, levofloxacin, ciprofloxacin, and piperacillin-tazobactam was lower, varying from 0.3 to 3.5%. Notably, 9.0% (<i>n</i> = 33) isolates exhibited multiple drug resistance, while 8.4% (<i>n</i> = 31) were resistant to florfenicol and/or azithromycin. Conjugation experiments demonstrated that resistance genes <i>floR</i> and/or <i>mph</i>(A) were transferred to the recipient strain <i>Escherichia coli</i> J53, leading to phenotypic resistance to florfenicol and/or azithromycin in the transconjugants. Whole genome sequencing (WGS) of STEC W24 identified that <i>floR</i> and <i>mph</i>(A) were located on a 77,016&#xa0;bp IncA/C type plasmid, designated as W24-<i>floR</i>-<i>mph</i>(A). A genetic structure with three IS<i>26</i> and one IS<i>6100</i> sequences flanking the multi-drug resistance region was detected, including two IS<i>26</i> copies adjacent to <i>floR</i>, <i>tet</i>(A), <i>aph(6)-Id_1</i>, <i>aph(3’’)-Ib_5</i>, <i>sul2</i> and <i>mph(A).</i></p> Conclusions <p>The findings highlight the presence of florfenicol and azithromycin resistance in bovine non-O157 STEC in Xinjiang, with <i>floR</i> and <i>mph</i>(A) genes residing on plasmids capable of horizontal transfer. Plasmids, transposons, and insertion sequences may mediate the dissemination of antimicrobial resistance genes.</p>

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Co-resistance and plasmid-mediated co-dissemination of florfenicol and azithromycin resistance in non-O157 Shiga toxin-producing Escherichia coli from cattle in Xinjiang, China

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月30日

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  • Lei Wang,
  • Xueqin Lan,
  • Yixin Bai,
  • Ying Huang,
  • Wanjing Jin,
  • Mengfei Zhang,
  • Xiaofeng Zheng,
  • Yi Zhang,
  • Xiaoli Du,
  • Yingyu Liu,
  • Xuelian Ma,
  • Mingyang Geng,
  • Zhanqiang Su,
  • Jinxin Xie,
  • Panpan Tong

摘要

Background

Florfenicol is a critical antibiotic used in cattle to manage respiratory infections, while azithromycin is recommended for treating early-stage Shiga toxin-producing Escherichia coli (STEC) infections. This study focused on examining the co-resistance and mechanisms of co-dissemination of resistance to florfenicol and azithromycin in 367 non-O157 STEC strains isolated from cattle in Xinjiang between 2015 and 2023.

Results

Among these isolates, 16.3% showed resistance, with drug resistance rates ranging from 5.4 to 10.6% for tetracycline, ampicillin, cefotaxime, streptomycin, sulfamethoxazole, florfenicol, aztreonam, azithromycin, gentamicin, ceftazidime, and piperacillin. Resistance to cefepime, ampicillin-sulbactam, amikacin, amoxicillin-clavulanic acid, levofloxacin, ciprofloxacin, and piperacillin-tazobactam was lower, varying from 0.3 to 3.5%. Notably, 9.0% (n = 33) isolates exhibited multiple drug resistance, while 8.4% (n = 31) were resistant to florfenicol and/or azithromycin. Conjugation experiments demonstrated that resistance genes floR and/or mph(A) were transferred to the recipient strain Escherichia coli J53, leading to phenotypic resistance to florfenicol and/or azithromycin in the transconjugants. Whole genome sequencing (WGS) of STEC W24 identified that floR and mph(A) were located on a 77,016 bp IncA/C type plasmid, designated as W24-floR-mph(A). A genetic structure with three IS26 and one IS6100 sequences flanking the multi-drug resistance region was detected, including two IS26 copies adjacent to floR, tet(A), aph(6)-Id_1, aph(3’’)-Ib_5, sul2 and mph(A).

Conclusions

The findings highlight the presence of florfenicol and azithromycin resistance in bovine non-O157 STEC in Xinjiang, with floR and mph(A) genes residing on plasmids capable of horizontal transfer. Plasmids, transposons, and insertion sequences may mediate the dissemination of antimicrobial resistance genes.