AUTHOR=Yao Xiaohui , Song Qiangqiang , Zhu Wei , Wei Jianchao , Shao Donghua , Liu Ke , Li Zongjie , Qiu Yafeng , Ma Zhiyong , Xia Lining , Li Beibei 

TITLE=Characterization of small plasmids carrying florfenicol resistance gene floR in Actinobacillus pleuropneumoniae and Pasteurella multocida isolates from swine in China

JOURNAL=Frontiers in Veterinary Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2023.1084491

DOI=10.3389/fvets.2023.1084491

ISSN=2297-1769

ABSTRACT=<p><italic>Actinobacillus pleuropneumoniae</italic> and <italic>Pasteurella multocida</italic> are two important bacterial pathogens in swine industry. In the present study, resistance profiles of nine commonly used antibiotics of <italic>A</italic>. <italic>pleuropneumoniae</italic> and <italic>P</italic>. <italic>multocida</italic> isolates of swine origin from different regions of China were investigated by determination of minimum inhibitory concentrations (MICs). In addition, genetic relationship of the florfenicol-resistant <italic>A</italic>. <italic>pleuropneumoniae</italic> and <italic>P</italic>. <italic>multocida</italic> isolates was determined by pulsed-field gel electrophoresis (PFGE). The genetic basis of florfenicol resistance in these isolates were explored by <italic>floR</italic> detection and whole genome sequencing. High resistance rates (&gt;25%) of florfenicol, tetracycline and trimethoprim- sulfamethoxazole were observed for both bacteria. No ceftiofur- and tiamulin- resistant isolates were detected. Furthermore, all the 17 florfenicol-resistant isolates (nine for <italic>A</italic>. <italic>pleuropneumoniae</italic> and eight for <italic>P</italic>. <italic>multocida</italic>) were positive for <italic>floR</italic> gene. The presence of similar PFGE types in these isolates suggested that clonal expansion of some <italic>floR</italic>-producing strains occurred in the pig farms from same regions. WGS and PCR screening showed that three plasmids, named pFA11, pMAF5, and pMAF6, were the cargos of the <italic>floR</italic> genes in the 17 isolates. Plasmid pFA11 exhibited novel structure and carried several resistance genes, including <italic>floR, sul2, aacC2d, strA, strB</italic>, and <italic>bla</italic><sub>ROB − 1</sub>. Plasmids pMAF5 and pMAF6 were presented in <italic>A</italic>. <italic>pleuropneumoniae</italic> and <italic>P</italic>. <italic>multocida</italic> isolates from different regions, suggesting horizontal transfer of the two plasmids are important for the <italic>floR</italic> dissemination in these <italic>Pasteurellaceae</italic> pathogens. Further studies of florfenicol resistance and its transfer vectors in <italic>Pasteurellaceae</italic> bacteria of veterinary origin are warranted.</p>