Molecular characterization of fluoroquinolone and/or cephalosporin resistance in Shigella sonnei isolates from yaks

Background: Members of the genus Shigella are intestinal pathogens and a major cause of seasonal outbreaks of bacterial diarrhea worldwide. Although humans are the conventional hosts of Shigella species, expansion of the Shigella host range to certain animals was recently reported. To investigate the prevalence of Shigella sonnei (S. sonnei) in yaks and perform molecular characterization, we analyzed 1132 fresh yak diarrhea! stool samples and collected a total of 44 S. sonnei isolates. Results: We performed multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) with Xbal-digested DNA to study genetic relatedness among the 44 isolates, which were differentiated into 4 sequence types (STs) and 32 PFGE types (PTs). All isolates harbored virulence genes, and 87.36% tested positive for invasion plasmid antigen H (ipaH), invasion associated locus (ial) and the Shigella enterotoxin gene sen. According to the results of antimicrobial susceptibility tests, 45.45% (20/44) were resistant to fluoroquinolones and/or cephalosporin. By sequencing the quinolone resistance determining region (QRDR) genes, we identified double mutations in gyrA (Ser83-Leu aid Asp87-Asn) and a single mutation in parC (Ser80-lle). All 12 fluoroquinolone-resistant S. sonnei isolates tested positive for the aac(6')-lb-cr gene but negative for qepA. Three isolates harbored qnr genes, including two with qnrS and one with qnrB. In addition, three types of beta-lactamase genes, bla(TEM-1), bla(OXA-1) and bla(CTX-M-4/79), were detected in cephalosporin-resistant isolates. Conclusions: The findings of this study have enriched our knowledge of fluoroquinolone- and/or cephalosporin-resistant S. sonnei isolates from yaks, which has important public health significance.