Theses and Dissertations
ORCID
https://orcid.org/0000-0003-2102-7176
Issuing Body
Mississippi State University
Advisor
Abdelhamed, Hossam
Committee Member
Lawrence, Mark L.
Committee Member
Pharr, G. Todd
Committee Member
Dinh, Thu
Date of Degree
12-13-2024
Original embargo terms
Complete embargo 2 years
Document Type
Dissertation - Open Access
Major
Veterinary and Biomedical Sciences (Infectious Disease)
Degree Name
Doctor of Philosophy (Ph.D.)
College
College of Veterinary Medicine
Department
Department of Comparative Biomedical Sciences
Abstract
Listeria monocytogenes is a resilient and highly adaptable foodborne pathogen, notorious for its ability to survive and grow in extreme environments, including refrigerated food products. L. monocytogenes not only thrives at low temperatures but also demonstrates the capacity to transition from a saprophytic lifestyle in the environment to a pathogenic state within host organisms. Understanding the molecular and regulatory mechanisms that enable L. monocytogenes to maintain membrane integrity, sustain energy production, and regulate virulence is crucial for developing strategies to control its persistence in food systems and its pathogenicity in humans. The mechanistic link between membrane integrity, cold adaptation, and virulence remains unexplored. This dissertation investigates the molecular and metabolic mechanisms that allow L. monocytogenes to maintain membrane integrity, adapt to cold stress, and regulate virulence under host-relevant conditions. The research spans multiple key areas, including the role of the branched-chain α-keto acid dehydrogenase (BKD) complex, phosphate acetyltransferase (Pta/Ptb), butyrate kinase (Buk), menaquinone biosynthesis, and the regulatory functions of PrfA. The study showed that disruption of the BKD complex resulted in a significant reduction in BCFA production, leading to impaired membrane integrity and reduced growth at low temperatures. The BKD-deficient strains also exhibited attenuated virulence, defects in intracellular replication, cell to cell spread, and phospholipase activity due to lower function of PrfA and its regulon. We also found that, Buk is essential for cold tolerance and deletion of buk resulted lower levels of BCFAs biosynthesis in mutant strain. Buk is also needed for full intracellular replication, cell to cell spread, phospholipase activity, and virulence of L. monocytogenes. We also revealed that L. monocytogenes might use alternative pathways instead of branched-chain amino acid (BCAAs) biosynthesis and degradation for fatty acid homeostasis. And lastly, our results demonstrated that disruptions in menaquinone biosynthesis, phosphate acetyltransferase, helicase, chemotaxis protein CheA, and ATP synthase significantly impaired bacterial growth at low temperatures. We discovered that menaquinone-deficient and Pta-disrupted mutants showed significant attenuation in virulence in the mouse model, even under PrfA active conditions. Our results provide a novel comprehensive exploration of the molecular pathways and regulatory networks that enable L. monocytogenes to adapt to cold environments and maintain virulence.
Recommended Citation
Chowdhury, Q M Monzur Kader, "Deciphering metabolic pathways that regulate membrane integrity and their impact on Listeria monocytogenes pathogenesis" (2024). Theses and Dissertations. 6430.
https://scholarsjunction.msstate.edu/td/6430