Fluoroquinolone Resistance Mechanisms in Shigella Isolates in Shanghai, China, Between 2010 and 2015.

OBJECTIVES: This study aimed to investigate the antimicrobial susceptibility of Shigella isolated in Shanghai, China and to determine the genetic basis of its resistance to fluoroquinolones. MATERIALS AND METHODS: A total of 402 strains of Shigella, including 145 Shigella flexneri and 257 Shigella sonnei isolates, were analyzed. The Kirby-Bauer disk diffusion method was used to determine the susceptibility of the strains to 13 antimicrobials. Minimum inhibitory concentration of ciprofloxacin was determined by E-test. Mutations within the quinolone resistance-determining regions (QRDRs) of gyrA and parC and in the plasmid-mediated quinolone resistance (PMQR) genes, including qnrA, qnrB, qnrS, and aac (6')-Ib-cr, were detected by polymerase chain reaction. All the products were then sequenced. RESULTS: Most of the Shigella isolates were found to be resistant to nalidixic acid (96.4%), streptomycin (96.4%), ampicillin (86.2%), tetracycline (79.8%), and sulfamethoxazole/trimethoprim (80.6%). S. flexneri isolates showed a significantly higher resistance to cefepime (33.6%), ciprofloxacin (54.2%), norfloxacin (34.1%), and levofloxacin (12.1%) compared with that observed for the S. sonnei strains (χ2 analysis, p < 0.05). Three mutations (Ser83, Asp87, and His211) in gyrA and one mutation (Ser80) in parC were detected. Of 257 S. sonnei isolates, 11.7% possessed gyrA mutations and 2% had parC mutations. Of 145 S. flexneri isolates, 98.6% possessed gyrA mutations and 97.9% had parC mutations. The plasmid-mediated resistance genes of qnrS and aac (6')-Ib-cr were detected among 17 strains (4.2%). CONCLUSIONS: The mutation percentage within the QRDR of S. flexneri was as high as 98.6 in gyrA and 97.9 in parC. The significant abundance of mutations within QRDRs conferred high levels of fluoroquinolone resistance. Moreover, the PMQR genes, particularly qnrS, played an important role in the decreased susceptibility of Shigella to fluoroquinolones.

[Characterization of phenotype and molecular characteristics on Vibrio cholerae strains isolated in Shanghai, 1962-2011].

OBJECTIVE: To describe the phenotype and molecular characteristics of Vibrio (V.) cholerae strains isolated in Shanghai, from 1962 to 2011. METHODS: K-B test was used to investigate the antibiotic resistance of V. cholerae strains. PCR was applied to detect seven virulence-related genes including cholera toxin (ctxA), zonula occludens toxin (zot), accessory cholera enterotoxin (ace), hemolysin (hlyA), toxin-coregulated pilus (tcpA) outer membrane protein (ompU) and the regulatory protein genes (toxR). Genetic relation was assessed by pulsed-field gel electrophoresis (PFGE) and the patterns were clustered by BioNumerics software. RESULTS: V. cholerae strains isolated from 1962 to 1996 were sensitive to most of the antibiotics. However, the strains isolated from 2005 to 2011 were resistant to many antibiotics. V. cholerae O139 group showed higher prevalence of resistance to several antibiotics compared with O1 group, and the resistance rate of the O139 toxigenic isolates was higher than that of the non-toxigenic isolates. Most of the O1 strains isolated from 2005 to 2011 were non-toxigenic while O139 strains isolated from 2005 to 2011 were almost toxigenic. There were no strains of ctxA+ detected from the rivers from 2005 to 2011. Main gene type of the O1 strains detected from the aquatic products was hlyA+ toxR+ ompU+, while that of the O139 strains was hlyA+ toxR+ ompU+ ctxA+ ace+ zot+ tcpA+. Using PFGE, 222 V. cholerae strains were subtyped into 121 molecular types. O139 strains were divided to three clusters and O1 strains to five clusters. CONCLUSION: The characteristics of V. cholerae strains isolated in Shanghai from 1962 to 2011 showed great changes, suggesting that more attention should be paid to the multiplication on antibiotic resistance of V. cholerae strains.