Mandy Sun | ALES Graduate Seminar

Date(s) - 29/01/2024
2:00 pm - 3:00 pm
3-18J Agricultural/Forestry Centre, University of Alberta, Edmonton AB

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Mandy Sun. This seminar is open to the general public to attend.

Zoom Link:

MSc with Dr. Lynn McMullen

Thesis Topic: Impact of carbohydrates and carnocyclin A on growth and gene expression of Listeria monocytogenes


Listeria 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 this organism is required to ensure the safety of these foods. Biopreservation techniques, such as bacteriocins (ribosomally synthesized antimicrobial compounds), are being researched as an alternative to chemical preservatives to control L. monocytogenes. Carnocyclin A, a class 1b bacteriocin, inhibits the growth of 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, strains of L. monocytogenes were grown in cooked ground beef supplemented with fructose, dextrose or sucrose, with or without addition of carnocyclin A. 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 done 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 done 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 was 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 strain of L. monocytogenes J1-177 suggests that the carbohydrate transport systems may be receptor molecules for carnocyclin A. However, the upregulation of the Mannose PTS system, sucrose phosphorylase, β-glucoside PTS system in other resistant isolates suggests that mechanism of resistance to carnocyclin A is dependent 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. Genes related to the carbohydrate transport systems, and those associated with sigma factors, cell wall synthesis and virulence, 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 and carbohydrate, 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.

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