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Impact of carbohydrates and carnocyclin A on growth and gene expression of Listeria monocytogenes
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- Author / Creator
- Sun, Man
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L. monocytogenes is the foodborne pathogen that causes listeriosis, which has a high fatality rate
of 20 to 30%. L. monocytogenes is often associated with ready-to-eat food products. Therefore,
techniques to control growth of this organism are needed for the safety of these foods.
Biopreservation techniques such as bacteriocins are being researched as an alternative to
chemical preservatives to control L. monocytogenes. Carnocyclin A is one of the bacteriocins
(class 1b) that can inhibit L. monocytogenes. The aim of this research was to investigate the
impact of carbohydrates on the development of resistance in strains of L. monocytogenes
exposed to carnocyclin A in cooked ground beef.
To determine the impact of carbohydrates and carnocyclin A, the strains of L. monocytogenes
were grown in cooked ground beef supplemented with 3 different carbohydrates (fructose,
dextrose and sucrose) with or without carnocyclin A and the growth was observed. The L.
monocytogenes isolates from the cooked ground beef were screened for resistance to carnocyclin
A. For the bacteriocin resistant isolates of L. monocytogenes, reverse transcription q-PCR was
carried out to determine the impact of carbohydrates and carnocyclin A on the expression of
genes involved in resistance. To determine the impact of carnocyclin A on the genomes of L.
monocytogenes, whole genome sequencing was performed to investigate the SNPs (single
nucleotide polymorphisms) of the parent strains (carnocyclin A sensitive) and resistant isolates
of L. monocytogenes.
The resistance of L. monocytogenes to carnocyclin A is both strain and carbohydrate dependent,
as evidenced by the different growth patterns. The downregulation of the Mannose PTS system
in the presence of dextrose for the resistant L. monocytogenes J1-177 strain suggests that the
carbohydrate transport systems are used as receptor molecules for carnocyclin A. However, the
upregulation of the Mannose PTS system, sucrose phosphorylase, β-glucoside PTS system in
other resistant isolates (L. monocytogenes J1-177 and L. monocytogenes C1-056 isolated from
meat supplemented with sucrose) suggests that mechanism of resistance to carnocyclin A is also
dependant on carbohydrate and strain. The high number of SNPs present in the resistant isolates
from cooked ground beef indicate that there is hypermutation of L. monocytogenes in response to
carnocyclin A. In addition, as the SNPs occurred not only in genes related to the carbohydrate
transport systems, but also in genes associated with cell wall and virulence, this suggests a more
general stress response to the presence of bacteriocins.
Overall, the L. monocytogenes resistance to carnocyclin A is mediated by factors such as strain
individuality and carbohydrate source, and mechanisms of resistance are broad rather than
specific. The results presented in this thesis will contribute to a more comprehensive
understanding on how carnocyclin A and the carbohydrates available in food products can
impact the resistance to bacteriocins and the mechanisms of resistance in L. monocytogenes. This
can then inform the use of bacteriocins in the food industry, particularly towards more effective
control strategies for L. monocytogenes in ready-to-eat meat products. -
- Subjects / Keywords
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- Graduation date
- Spring 2024
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.