Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Immunology and Microbiology

First Advisor

Melody N. Neely

Abstract

The systemic pathogens Streptococcus agalactiae (GBS) and Streptococcus pneumoniae remain a significant threat to human health worldwide. The ability of these organisms to cause systemic disease is compounded by the production of a polysaccharide capsule that provides immune evasion function. The production of the polysaccharide capsule in systemic streptococcal pathogens is controlled in part by the membrane bound protein CpsA. These studies analyze the contribution of CpsA to regulation of capsule level in the model aquatic pathogen Streptococcus iniae and human specific pathogen GBS, and how this regulation affects virulence in in-vitro, ex-vivo, and in-vivo models of pathogenesis. We have determined that the membrane topology of the CpsA protein consists of a small cytoplasmic N-terminus, and a large extracellular C-terminus that contains the conserved DNA_PPF and LytR protein domains. The cytoplasmic N-terminal region in its entirety is capable of binding specifically to the capsule operon cpsA promoter in S. iniae, and to two putative promoter elements in GBS which include the capsule operon cpsA promoter and the internal cpsE promoter. Additionally, CpsA is a modular protein, with the cytoplasmic N-terminus as a capsule-activating domain, the DNA_PPF region as a capsule-repressing domain, and the LytR region as a control domain that regulates the activities of the other two domains. CpsA also appears to regulate cell wall maintenance, as truncation or removal of CpsA results in longer chains of cocci in both S. iniae and S. agalactiae, a phenotype that is associated with altered antimicrobial resistance and autolysis activity in S. iniae. Taken together, CpsA contributes to the complex regulatory scheme controlling capsule and cell wall, the two major constituents of bacterial cell surface macromolecular structure, and does so in a way that influences pathogenesis during systemic disease. The insights gained through these studies indicates that CpsA can be targeted in a way that is detrimental to bacterial survival in the context of systemic disease, suggesting CpsA may be an important future target of anti-virulence antimicrobial therapy.

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