Antimicrobial resistance and genetic characterization of Shigella spp. in Shanxi Province, China, during 2006–2016

Background Shigella spp., facultative anaerobic bacilli of the family Enterobacteriaceae , are one of the most common causes of diarrheal diseases in human worldwide which have become a significant public health burden. So, we aimed to analyze the antimicrobial phenotypes and to elucidate the molecular mechanisms underlying resistance to cephalosporins and fluoroquinolones in Shigella isolates from patients with diarrhea in Shanxi Province. Results During 2006–2016, we isolated a total of 474 Shigella strains (including 337 S. flexneri and 137 S. sonnei ). The isolates showed high rates of resistance to traditional antimicrobials, and 26, 18.1 and 3.0% of them exhibited resistance to cephalosporins, fluoroquinolones and co-resistance to cephalosporins and fluoroquinolones, respectively. Notably, 91.1% of these isolates, including 22 isolates that showed an ACTSuT profile, exhibited multidrug resistance (MDR). The resistance rates to cephalosporins in S. sonnei isolates were higher than those in S. flexneri. Conversely, the resistance rates to fluoroquinolones were considerably higher in S. flexneri isolates. Among the 123 cephalosporins-resistant isolates, the most common extended-spectrum beta-lactamase gene was bla TEM-1 , followed by bla CTX-M , bla OXA-1 , and bla SHV-12 . Six subtypes of bla CTX-M were identified, bla CTX-M-14 ( n = 36) and bla CTX-M-55 ( n = 26) were found to be dominant. Of all the 86 isolates with resistance to fluoroquinolones and having at least one mutation (Ser83Leu, His211Tyr, or Asp87Gly) in the the quinolone resistance-determining regions of gyr A, 79 also had mutation of par C (Ser80Ile), whereas 7 contained plasmid-mediated quinolone resistance genes including qnr A, qnr B, qnr S, and aac(60)-Ib-cr. Furthermore, pulsed-field gel electrophoresis analysis (PFGE) showed a considerable genetic diversity in S. flexneri isolates. However, the S. sonnei isolates had a high genetic similarity. Conclusions Coexistence of diverse resistance genes causing the emergence and transmission of MDR might render the treatment of shigellosis difficult. Therefore, continuous surveillance might be needed to understand the actual disease burden and provide guidance for shigellosis.