Prevalence and Characterization of Fluoroquinolone Resistant Salmonella Isolated From an Integrated Broiler Chicken Supply Chain

Abstract

The objectives of this study were to investigate the prevalence and fluoroquinolone resistant <i>Salmonella</i> isolated from an integrated broiler chicken supply chain and their molecular characterization. In total, 73 <i>Salmonella</i> isolates were recovered from a broiler chicken supply chain in Shanghai. <i>Salmonella</i> isolates were tested for susceptibility to 11 antimicrobial agents using the broth dilution method and were characterized using pulsed-field gel electrophoresis (PFGE). Then, the <i>Salmonella</i> isolates were examined for mutations in quinolone resistance-determining region (QRDR) of <i>gyrA</i>, <i>gyrB</i>, <i>parC</i>, and <i>parE</i>, and were screened for plasmid-mediated quinolone resistance (PMQR) genes. Lastly, we sequenced the plasmids carrying <i>qnrS1</i> in six <i>Salmonella</i> isolates from three sources (two isolated per source). Among 73 <i>Salmonella</i> isolates, 45 isolates were identified as <i>S</i>. Indiana, 24 were <i>S</i>. Schwarzengrund, 2 were <i>S</i>. Enteritidis, and 2 were <i>S</i>. Stanleyville. In addition, high rates of resistance were detected for nalidixic acid (41.1%) and ciprofloxacin (37.0%), while resistance to other test agents was diverse (2.0-100%). <i>S</i>. Indiana and <i>S</i>. Schwarzengrund isolates from different sources exhibited the same PFGE pattern, suggesting that the <i>Salmonella</i> isolates possessed high potential to spread along the broiler chicken supply chain. <i>gyrA</i> and <i>parC</i> exhibited frequent missense mutations. Moreover, <i>qnrS1</i> was the most prevalent PMQR gene in the 73 <i>Salmonella</i> isolates, and it was found about a new hybrid plasmid. This study concludes a high prevalence of fluoroquinolone resistant <i>Salmonella</i> in chicken supply chain, threatening the treatment of <i>Salmonella</i> foodborne diseases. In particular, the emergence of a new hybrid plasmid carrying <i>qnrS1</i> indicates that the recombination of plasmid carrying resistance gene might be a potential risk factor for the prevention and control strategies of drug resistance.