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Permanent link (DOI): https://doi.org/10.7939/R3PS68

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Effect of bacterial stress response on pathogen enumeration and its implications for food safety Open Access

Descriptions

Other title
Subject/Keyword
bacterial stress response
food safety
pathogen enumeration
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Wang, Huaiyu
Supervisor and department
Bressler, David (Agricultural, Food and Nutritional Science)
Examining committee member and department
McMullen, Lynn (Agricultural, Food and Nutritional Science)
Raivio, Tracy (Biological Sciences)
Gänzle, Michael (Agricultural, Food and Nutritional Science)
Department
Department of Agricultural, Food, and Nutritional Science
Specialization

Date accepted
2010-11-04T15:58:43Z
Graduation date
2011-06
Degree
Master of Science
Degree level
Master's
Abstract
To determine the impact of stress response on enumeration, cell association status and the viability of Escherichia coli DH5α, Staphylococcus aureus ATCC 13565 and Listeria monocytogenes CDC 7762 were evaluated using fluorescence microscopy and were compared with the outcomes of traditional plate count and optical density measurements. Fluorescence microscopy revealed that organic acid stress (acetic and lactic, pH 2.7-3.3) induced cell clumping with little loss of viability in Escherichia coli DH5α. Significantly lower values for cell enumeration were found for plate counts and OD600 measurement, likely due to cell clumping in response to organic acid stress. Gram-negative bacteria Escherichia coli DH5α showed higher levels of clumping and subsequent resistance against organic acid stress. Increased cell surface hydrophobicity was found in cells that exhibited more evident clumping. However, inorganic acid stress (hydrochloric and sulfuric, pH 3.0-3.3) induced only very low level of clumping in stationary-phase Escherichia coli DH5α and almost no clumping in other cultures. Osmotic stress, heat and cold shock were not found to induce cell clumping. It has been determined that traditional enumeration methods have significantly underestimated the number of viable bacterial cells when organic acid stress is involved. Plate counts and OD600 measurement therefore need to be reassessed as tools for accurate evaluation of pathogens in food industry.
Language
English
DOI
doi:10.7939/R3PS68
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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