Adaptation of Listeria monocytogenes to food processing environments

Omelchenko, Oleksii (2025) Adaptation of Listeria monocytogenes to food processing environments. Doctoral thesis, University of East Anglia.

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Abstract

Despite rigorous cleaning and disinfection regimes, food production environments (FPE) can still harbour Listeria monocytogenes, a significant concern to food manufacturers and health authorities due to the high mortality rate associated with invasive listeriosis. Mechanisms contributing to L. monocytogenes persistence in FPE are proposed to include biofilm formation and reduced susceptibility to biocides, such as benzalkonium chloride (BC). We hypothesised that prolonged exposure to these disinfectants and other FPE-associated stressors would drive L. monocytogenes adaptation, resulting in the accumulation of genetic mutations linked to biofilm formation and reduced biocide susceptibility. To test this, I developed a biofilm persistence model and conducted 30 sequential passages of biofilm-associated cells under subinhibitory BC concentrations. Whole-genome sequencing of evolved populations, observed fixed concurrent mutations across independent experimental lineages, identifying mechanisms associated with persistence and niche adaptation. Reduced BC susceptibility arose through multiple independent mutations in the fepRA operon, encoding the FepR transcriptional repressor and the FepA MATE efflux pump. These mutations conferred comparable levels of reduced BC susceptibility in both planktonic and biofilm lifestyles. Fixed mutations associated with biofilm growth mapped to several loci, including the ykoK riboswitch and downstream mgtA metal transporter, the pyrimidine biosynthesis operon, and the stress response-related rsb operon. For the loci most affected by mutations, I constructed a panel of deletion mutants, and phenotypic analyses revealed that ΔrsbU (stress response), exhibited reduced biofilm thickness, with biovolume significantly decreased in ΔrsbU and ΔpyrD (nucleotide synthesis) mutants. In addition, distinct biofilm morphologies were observed in ΔrsbU and ΔmgtA (metal homeostasis) mutants, which displayed web-like filaments and a porous extracellular matrix, respectively. Collectively, these findings provide new insights into the mechanisms underlying L. monocytogenes biofilm persistence and reduced biocide susceptibility in the context of FPE, and reveal novel targets potentially exploited by L. monocytogenes to establish and maintain niches in unfavourable environments.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Medicine and Health Sciences > Norwich Medical School
Depositing User:	Chris White
Date Deposited:	31 Mar 2026 10:42
Last Modified:	31 Mar 2026 10:42
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102664
DOI:

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