Impact of carbohydrates and carnocyclin A on growth and gene expression of Listeria monocytogenes
Creators: Sun, Man
Publisher: name: University of Alberta Library
Year: 2024

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