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

Abstract

To describe the phenotype and molecular characteristics of Vibrio (V.) cholerae strains isolated in Shanghai, from 1962 to 2011. 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. 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. 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.