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Browsing Research Articles (DFST) by Author "Shikongo-Nambambi, Martha N."

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    Control of bacterial contamination during marine fish processing
    (Macrothink Institute, 2012) Shikongo-Nambambi, Martha N.; Shoolongela, Abrahams S.; Schneider, Martin B.
    Fish is a vital source of nutrients to humans due to its proteinaceous nature, high content of unsaturated fatty acids and low contents of carbohydrates. In their natural environments fish are exposed to a myriad of microorganisms some of which compromise the shelf life of the product and/or safety in humans. Most fish factories located along coasts find it economical to use processed sea water during processing. Processed sea water however can be a source of microbial contamination to fish. Fish factories are also vulnerable to biofilm formation on surfaces and within water distribution pipes. Biofilms result from bacterial attachment and growth in aqueous environments that render bacteria resistant to sanitising agents. This article reviews the conditions permissible to bacterial contamination in marine fish factories. The role of water in bacterial contamination and survival has been highlighted. Bacterial pathogens commonly associated with fish factories and their survival strategies have also been discussed. The use of selected sanitizing agents and UV irradiation in marine fish processing have been explored. The fundamental antimicrobial mechanisms of chlorine, ozone and H2O2 is the generation of toxic metabolic intermediates that damage microbial structural and functional components, causing metabolic paralysis and cell death. UV radiation damages DNA hindering gene expression processes. Controlling bacteria biofilm has been well experimented in fresh water systems, but knowledge about disinfection of marine waters is still lacking. The review concludes that in order to optimise the microbiological quality of marine fish, suitable disinfectants effective in sea water need to be authenticated.
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    Identification of putative vibrio species isolated from processed marine fish using Thiosulphate-Citrate-Bile-Sucrose (TCBS), Agar
    (School Domain International, 2012) Shikongo-Nambambi, Martha N.; Chimwamurombe, Percy M.; Venter, Stephanus N.
    Aims: To identify putative Vibrio isolates obtained from processed hake, pilchards and horse mackerel using Thiosulphate-Citrate-Bile-Sucrose (TCBS) agar.Place and Duration of Study: Sampling during April – June 2005 in Walvis Bay Namibia. Further analyses performed at the Department of Microbiology and Plant Pathology, University of Pretoria, South Africa between 2005 and 2007. Methodology: The 247 putative Vibrio isolates obtained from Thiosulphate-Citrate-Bile- Sucrose (TCBS) agar were initially grouped according to their Gram, oxidase and oxidation-fermentation reactions. Thereafter PCR was used to screen the isolates for genes specific to human pathogenic Vibrio species such as Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus. This was followed by sequencing the 16S rRNAgene for isolates of interest and drawing Neighbour Joining phylogenetic trees based on the data. All atypical isolates were further characterised by a combination of selected phenotypic tests and the V. alginolyticus specific collagenase gene PCR. Results: Of the 247 isolates obtained from TCBS, four were Gram positive. Many of the Gram negative isolates belonged to the family Enterobacteriaceae and others were members of the Pseudomonadaceae. Of the 91 isolates identified as belonging to the Vibrionaceae and related families, Vibrio alginolyticus was the dominant Vibrio species. None of the bacteria isolated from the processed fish belonged to the human pathogenic Vibrio species. Conclusion: This study again demonstrated that TCBS agar is not selective for the isolation of Vibrio species and that a wide range of bacteria could be isolated on this medium when analysing marine fish. The identity of putative Vibrio isolates obtained from this medium should therefore be confirmed employing a number of phenotypic and genetic techniques to accurately identify the atypical isolates.
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    The role, isolation and identification of Vibrio species on the quality and safety of seafood
    (Academic Journals, 2012) Shikongo-Nambambi, Martha N.; Petrus, Ndilokelwa P.; Schneider, Martin B.
    Seafoods in their natural environments are associated with a variety of microorganisms. Fish shelf life reduction results from microbial metabolism, mainly by Gram negative bacteria that produce chemical compounds responsible for bad odour, texture and taste. Shelflife is estimated by performing total viable bacterial counts at ambient and refrigeration temperatures. The type and number of bacteria present on seafood depends on the microbial composition of the surrounding waters, on the intrinsic factors, extrinsic factors, processing, and implicit factors and on the microbial interactions within the fish itself. Although, sea food safety assessment is preferably determined by detecting indicator organisms; such as Enterobacteriaceae and coliforms, none of these groups fulfil all requirements that guarantee food safety necessitating direct detecting of relevant pathogens. Vibrio species are part of the bacteria genera associated with seafoods borne diseases. Prompt and accurate detection and identification methods of pathogens are imperative to determine the product compliance with seafood microbiological criteria. Although cultural methods have long been used in detecting human pathogens including Vibrio species in fish, these methods are time consuming and sometimes inaccurate. Also some pathogens have the propensity to change into the Viable but non culturable (VBNC) state in unfavourable environments. The use of molecular methods is hampered by drawbacks, such as inter species 16S rRNA sequence similarity and that some strains carry multiple copies of the 16S rRNA gene. A combination of classical, numerical taxonomy and Multi locus sequence analysis (MLSA) methods are promising to give absolute resolution between closely related Vibrio species.