Virulence genes and susceptibility to antimicrobial agents and heavy metals of Vibrio cholerae isolated from aquaculture water farming Litopenaeus vannamei

Abstract:

The aim of this study was to investigate virulence genes and susceptibility to antimicrobial agents and heavy metals of Vibrio cholerae strains isolated from aquaculture water farming Litopenaeus vannamei, in order to provide scientific data support for early warning of food-borne and life-threatening cholera disease caused by V. cholerae. The genes involved in pathogenicity and integrative conjugative elements (ICEs) were detected by polymerase chain reaction (PCR). The virulence-related genes were absent in all V. cholerae isolates, including ctxAB, sto, tcpA, ace and zot. However, all the isolates were tested positive for a toxR gene, 19.05% of which also contained a rtxA gene. Some of the functional genes (int, traI, traC, setR, attR) involved in conserved module structures of SXT-R391 family ICEs were detected positive, suggesting no possible transfer activity of the ICEs detected in the isolates. Antimicrobial susceptibility of V. cholerae strains were examined by using standard Kirby Bauer disk diffusion method according to the Clinical and Laboratory Standards Institute (USA,2010 Edition),showing distinct susceptibility to ten antimicrobial agents belonging to six drug classes tested.Total 13.10% and 2.38% of the V. cholerae strains were resistant to ampicillin and gentamycin, respectively. About 25.00%-1.19% of the isolates also displayed intermediate resistance to rifampicin, streptomycin, ampicillin, kanamycin and spectinomycin. In addition, a narrow heavy metal resistance profile was detected in the isolates tested, showing strong resistance to Pb and Zn. By pulsed-field gel electrophoresis (PFGE) genetyping, these V. cholerae isolates were clustered into five NotI-PFGE types and thirteen subtypes with 56%-100% identity. The data in this study constituted the first evidence for molecular and resistance phenotype characterization of the V. cholerae isolates of aquaculture environmental origin.