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Some aspects of the ecology of Listeria monocytogenes in salmonid aquaculture


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Tienungoon, Suwunna 1998 , 'Some aspects of the ecology of Listeria monocytogenes in salmonid aquaculture', PhD thesis, University of Tasmania.

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In this thesis, several related aspects of the ecology of Listeria spp. especially L. monocytogenes
in aquatic environments and foods were studied.
The ecology of the organisms in aquatic habitats was investigated in North West Bay,
southern Tasmania, over a 12 month period. Listeria spp. most frequently occurred in
effluent and river water but less often in receiving estuarine waters. Sediments and
shellfish served as a better reservoir for the organisms. Recent rainfall and the level of
faecal coliforms and E. coli were the most significant variables (P ≤ 0.01) related to the
presence/absence of Listeria species and L. monocytogenes in estuarine water.
Secondly, the relationship between the occurrence of the human pathogenic species, L.
monocytogenes, in aquatic environments and in a nearby salmon processing plant and its
products was studied. Molecular subtyping methods (multilocus enzyme electrophoresis
and repetitive sequence element-PCR) were employed to help trace the distribution of L.
monocytogenes strains. A high diversity of L. monocytogenes was found in the aquatic
environment but only a small group was detected in fish and the fish processing
Thirdly, to be able to understand the physiology and growth response of L. monocytogenes
to temperature, water activity, pH, and lactic acid and which in tum may be
used to minimise the consequences of contamination by the pathogen of foods,
quantitative microbiology (predictive microbiology) studies were conducted. The results
were incorporated into 2 different types of mathematical model. The first type of model,
a kinetic model, was developed using a "square root type model" which is useful for
predicting the shelf-life of foods. The second type of model, a probability model (a so called
"growth/ no growth interface" model) which is a novel model for L. monocytogenes
growth limits was developed using a new approach, viz "generalised nonlinear
regression method". This type of model is useful for predicting the condition when
micro-organisms, especially pathogenic bacteria, might grow or might not grow.
Finally, model predictions were evaluated by comparing them to novel and literature data
broadly relevant, to the range of conditions in foods for which the models were
developed. Limited tests, involving direct addition of different levels of lactic acid onto
traditional cold-smoked salmon products were performed as an approach to non-thermal
inhibition or inactivation of L. monocytogenes and also to test the performance of the

Item Type: Thesis - PhD
Authors/Creators:Tienungoon, Suwunna
Keywords: Aquaculture, Salmon industry, Salmonidae, Listeria monocytogenes
Copyright Holders: The Author
Copyright Information:

Copyright 1998 the Author. The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s) - Copyright the Author

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

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