Wide dissemination of multidrug-resistant Shigella isolates in China.

Objectives: To evaluate the prevalence of antimicrobial resistance and selected antimicrobial resistance mechanisms in Shigella isolates recovered in outpatients from 1997 to 2009 in China. Methods: The isolates were subjected to serotyping and antimicrobial susceptibility testing. Shigella isolates producing extended-spectrum beta-lactamases (ESBLs) or resistance to ciprofloxacin were further characterized by PFGE to determine the genetic relatedness. These isolates were also screened for beta-lactamase genes and mutations in the quinolone resistance-determining regions (QRDRs) by PCR. DNA sequence analysis was also performed. Results: After serotyping, 301 Shigella isolates were grouped into three subgroups and 13 distinct serotypes. The antimicrobial resistance profiles differed among subgroups and serotypes. Ciprofloxacin-resistant isolates were mainly Shigella flexneri serotypes f2a and f4a, which were resistant to at least four additional non-quinolone antimicrobials. Three point mutations in the QRDRs of gyrA and parC were identified in all 30 ciprofloxacin-resistant S. flexneri isolates. Plasmid-mediated bla(CMY 2), bla(CTX M 14), bla(CTX M 15) and bla(CTX M 55)-like genes were found in 29 ESBL-producing isolates and three clavulanic-acid-resistant isolates, and six isolates also exhibited resistance to ciprofloxacin. Distinct genetic differences in both serotypes and PFGE profiles were observed for these ciprofloxacin-or extended-spectrum-cephalosporin-resistant isolates. Conclusions: ESBL-producing or fluoroquinolone-resistant Shigella is no longer an unusual phenomenon in the local community. The monitoring programme in China should stay vigilant to the dissemination of these isolates and the health agencies must take appropriate measures to restrict the abuse of antimicrobials, especially in the community.