The use of Genome Wide Association Studies to understand two key aspects of Staphylococcus aureus pathogenesis

: serum resistance and toxicity.

Abstract

Staphylococcus aureus is a significant threat to global health with over 150,000 cases of invasive disease in Europe alone annually. This is due to a variety of reasons including the diverse arsenal of virulence factors possessed by the bacterium, and the rapid emergence of antibiotic resistance strains. This is confounded by S. aureus being associated with relapsing infections, and the immune system failing to give lasting immunity. If we are to better govern S. aureus infections and discover novel therapeutics, concerted interdisciplinary approaches to studying pathogenesis need to be attempted. The work presented in this thesis represents such an approach, mixing molecular biology, mathematical biology, bioinformatics, and biochemistry to study two key aspects of S. aureus pathogenicity: serum resistance and toxicity. This has led to the identification of MpsB, a novel effector of serum resistance due to this proteins role in generating membrane potential. This protein was also found to affect the production of cytolytic toxins, describing for the first time a possible link between membrane potential and activation of the Agr system. Using functional genomics in the form of a Genome Wide Association study we have found 6 previously undescribed contributors to serum resistance. Extensive molecular characterisation of one of these hits, TcaA, yielded the discovery of a unique mechanism of serum resistance involving the ligation of wall teichoic acid into the cell envelope. Previous study of this protein found an association with teicoplanin resistance. We have also unravelled the mechanism behind this phenotype and found it to involve the contribution of this protein to cross-linking the peptidoglycan cell wall. The final work in this thesis worked on characterising previous GWAS hits found to be involved in toxin production. Work on one of these, SpoIIIE, found that when this protein was inactivated there was a shut-down of the Agr system due to the action of the SOS response.

Date of Award	12 May 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ruth C Massey (Supervisor)