Author: Fok, Wai-pang Stephen
Title: Molecular characterization of vibrio cholerae non-01, non-O139 strains isolated from food and environmental samples in Hong Kong
Degree: M.Sc.
Year: 2003
Subject: Cholera -- Diagnosis
Vibrio cholerae
Pathogenic bacteria -- Identification
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
School of Nursing
Pages: ix, 76 leaves : ill. (some col.) ; 30 cm
Language: English
Abstract: Cholera is a severe diarrheal disease caused by Vibrio cholerae serotype O1. Since the emergence of the new epidemic strain known as Vibrio cholerae serotype O139, the significance of other non-O1, non-O139 Vibrio cholerae strains in the environment has attracted the attention of scientists. The marine ecosystem is the natural habitat for Vibrio cholerae strains. It is due to their autochthonous nature in marine ecosystem that a lot of non-O1, non-O139 Vibrio cholerae strains were isolated in the Vibrio cholerae surveillance program from raw seafood and water samples, conducted by the public health laboratories, Department of Health, Special Administrative Region, Hong Kong. The virulence potential of Vibrio cholerae depends on the types of virulence-associated factors these bacteria possess. However, no study has yet been conducted to examine the virulence potential of these isolates in view of their virulence-associated genes. In this study, an improved multiplex polymerase chain reaction (PCR) and singleton PCRs based on the protocol of Rivera et al (2001) and singleton PCRs were utilized to characterize 267 environmental and 15 clinical isolates of non-Ol, non-O139 Vibrio cholerae by examining their virulence-associated genes. The genes analysed were ctxA, hlyA, ompU, stn/sto, tcpA, tcpI, toxR and zot. Five genotypes, designated as I, II, IIa, III and IV, were obtained according to the virulence-associated genes the bacteria possessed. None of the isolates carried the gene encoding the potent cholera toxin CTX or others such as tcpA, tcpI, zot genes. All the isolates possessed the hlyA and the toxR genes. Three of the five genotypes (I, II and IIa) were most frequently observed among environmental isolates (mainly fish tank water samples and raw seafood). These three genotypes were also detected in the clinical isolates. Since the clinical strains in this study did not possess the CTX and Zot encoding genes, their pathogenicity may be due to individual patient's susceptibility or other unknown mechanisms. The environmental strains were of low virulence potential. However, continuous monitoring on the virulence-associated gene reservoir is of public health interest. The PCRs described here will be useful tools for this purpose. In this study, the information collected on the virulence-associated genes forms a useful reference for further studies on the virulence of both environmental and clinical isolates. DNA sequencing was performed on 17 of the hlyA48l amplicons of the hlyA gene to examine the polymorphisms in this amplicon sequence. SSCP analysis was also performed on these 17 selected PCR products. Eleven sequence groups were revealed by DNA sequence analysis, and could not be differentiated completely by SSCP analysis. Since the hlyA48l amplicon was polymorphic, DNA sequencing of this amplicon would be a useful tool in following the evolution of non-O1, non-O139 Vibrio cholerae strains.
Rights: All rights reserved
Access: restricted access

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