Theses and Dissertations

Ting Zhang

Issuing Body

Mississippi State University

Advisor

Wang, Chinling

Committee Member

Seo, Keun Seok

Committee Member

Pruett, Stephen B.

Committee Member

Pinchuk, Lesya M.

Committee Member

Pharr, G. Todd

Date of Degree

8-17-2013

Document Type

Dissertation - Open Access

Major

Veterinary Medical Science

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Department

Veterinary Medical Science Program

Abstract

The pathogenicity of food-borne intracellular bacterium Listeria monocytogenes is greatly associated with its abilities to invade non-phagocytic cells, counteract the host innate immune system, resist bactericidal antibiotic-mediated killing, and breaking the physical barriers. In the last 30 years of research on L. monocytogenes, several virulence factors, such as Listeriolysin O (LLO), InlA, InlB, ActA, PI-PLC, and PC-PLC have already been characterized as important players that help this bacterium to achieve the key stage of infection. There are approximately 3,000 open reading frames in Listeria’s genome; however, only few virulence factors are functionally characterized. Thus, it is important to identify new virulence factors and understand how new virulence factors in Listeria help this opportunistic pathogen to counteract the host innate immune system, resist antibiotic-mediated killing, colonize vital organs, and finally successfully develop life-threatening listeriosis. In this study, inrame deletion mutagenesis was used to generate the deletion mutants of novel listerial virulence factors and a series of biochemical, in vitro and in vivo experiments were conducted to characterize the roles of these virulence factors during the infection process. In the first part of this study, an AlkD-like protein (Adlp, LmoF2365_0220) was identified and the protein is associated with oxidant tolerance and aminoglycoside antibiotic resistance. In the second part of this study, a new internalin-like protein (LmoH7858_0369) was shown to be involved in invasion of Hep-G2 cells and organ colonization in mice. The third part of this study showed that listeriolysin O (LLO) mediates cytotoxicity on brain endothelial cells, suggesting that LLO may contribute to the invasion of the central nervous system by L. monocytogenes. In summary, we identified and characterized two novel virulence factors, Adlp and LmoH7858_0369 that contributed to bacterial infection and revealed a new invasion mechanism of CNS cells that is mediated by LLO. Results from these studies provide a better understanding on the pathogenicity of L. monocytogenes and can be used as therapeutical targets or vaccine candidates

URI

https://hdl.handle.net/11668/20246

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