Title page for ETD etd-10192011-105909

Document Type Doctoral Thesis
Author Shikongo-Nambabi, Martha Naita Namwaala Nangulohi
Email mnambabi@unam.na
URN etd-10192011-105909
Document Title Occurrence and control of Vibrio species as contaminants of processed marine fish
Degree PhD
Department Microbiology and Plant Pathology
Advisor Name Title
Dr P M Chimwamurombe Co-Supervisor
Prof S N Venter Supervisor
  • processed marine fish
  • Vibrio species
  • contaminated seafood
Date 2011-09-09
Availability unrestricted
Marine water contains large numbers of fish spoilage bacteria and pathogens including V. cholerae, V. parahaemolyticus, and V. vulnificus. Consumption of contaminated seafood could lead to the transmission of these pathogens to humans. Accurate identification of suspected pathogens and spoilage organisms is important to ensure consumer safety and a long shelf life. This project assessed the bacterial quality of hake during processing. Some attention was also given to pilchards and horse mackerel. The results showed a sharp increase in the mesophilic and sucrose fermenting Vibrio species counts in hake after filleting. It has been suggested that this contamination occurred during processing from biofilms present in the sea-water distribution system.

During the study 257 strains isolated from Thiosulphate citrate bile salts sucrose (TCBS) agar were screened to determine the presence of the pathogenic Vibrios amongst these isolates. It was difficult to distinguish between V. alginolyticus and V. parahaemolyticus species due to high sequence similarity in their 16S rRNA genes. Final identification of the isolates required a polyphasic approach and it was found that none of the pathogenic Vibrios were present but that the Vibrio isolates mainly belonged to V. alginolyticus.

As it was suspected that the main source of contamination was the treated sea water used during processing the ability of chlorine, ozone and hydrogen peroxide to prevent biolfilm formation was examined. The behaviour of two V. alginolyticus strains (V590 and V595) isolated from the processed hake was evaluated. These strains formed biofilms faster than the V. alginolyticus LMG4409 type strain, but were similar to V. parahaemolyticus LMG2850. Biofilms formed by these bacteria were resistant to 4 mg/l chlorine and to 2 mg/l ozone, but were inhibited by 0.05 % and 0.2 % hydrogen peroxide for biofilms initiation and mature biofilms respectively. The close resemblance of atypical V. alginolyticus isolates to V. parahaemolyticus may indicate the ability of pathogens to survive under similar conditions. Effective decontamination and quality assurance strategies are therefore required when processing fish to prevent disease outbreaks.

2010 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Shikongo-Nambabi, MNNN 2010, Occurrence and control of Vibrio species as contaminants of processed marine fish, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-10192011-105909/ >


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