Increasing clinical resistance rate of Shigella sonnei to cefotaxime in Jiangsu Province, China, between 2012 and 2015

Background: The objective of this study is to evaluate the prevalence of Shigella sonnei (S. sonnei) and characterize the mechanism of its increasing resistance to cefotaxime, a third-generation cephalosporin agent between 2012 and 2015. Methods: We investigated the drug resistance in 95 isolates of S. sonnei by K-B dilution method and isolates with the extended-spectrum beta-lactamases (ESBLs)-producing genes were detected by polymerase chain reaction (PCR) and sequencing. Results: Over a 4-year period, the resistance rate of S. sonnei to cefotaxime increased from 31.6% to 64.3%, between 2012 and 2015. Molecular characterization of the ESBL genes, comprising 28 strains of CTX-M-1 group: blaCTX-M-55 (n=22), blaCTX-M-3 (n=3) and blaCTX-M-15 (n=3); 11 strains of CTX-M-9 group: blaCTX-M-14 (n=9) and blaCTX-M-65 (n=2), and 36 strains with blaTEM-1 gene. None of S. sonnei isolates carried blaCTX-M-2 group and SHV-type. Conclusions: The antimicrobial resistance rate of S. sonnei to cefotaxime significantly increased. Accordingly, regular surveillance of the cephalosporin-resistant S. sonnei should be emphasized. Moreover, exploration of the mechanism underlying the resistance of S. sonnei to cefotaxime contributes to the prophylaxis of further emergence of drug resistance.