Staphylococcus aureus is asymptomatically carried in approximately 30% of the population, which is a risk for subsequent infections. S. aureus produces a vast array of virulence factors, leading to varied infections. In this project, a functional genomics approach was used to try and gain further insights into how this pathogen regulates its virulence. First, a result from a Genome Wide Association Study (GWAS) investigating the link between genotypic variation and variation in toxin production showed a link between mupirocin resistance and toxin production. Second, a group of clinical Methicillin-Resistant S. aureus (MRSA) isolates of the ST239 lineage were screened for variation in lipase activity, and a GWAS was carried out using this data. Mupirocin is an antibiotic which targets isoleucyl-tRNA synthetase, which binds isoleucine to its tRNA to form isoleucyl-tRNA. The mutation associated with toxin production in the GWAS was shown to increase the presence of free isoleucine in mupirocin resistant S. aureus cells, suggesting that there was less isoleucyl-tRNA. This would be expected to affect proteins which are high in isoleucine, of which AgrC is one; this is part of the accessory gene regulator (agr) system, which controls virulence. Initially, AgrC is translated slower in mupirocin resistant strains, however there is no difference in overall agr activity at later time points. It was also found that competitive fitness of mupirocin resistant strains lacking the agr system is lower, therefore lowering toxin production seems to alleviate the fitness cost of this mutation. The GWAS carried out on lipase production resulted in a list of genes, three of which were taken for further investigation - these were SAUSA300_1966, murA and atpH. SAUSA300_1966 is a putative phage-antirepressor protein, which may also repress lipase or interact with a lipase repressor. murA is part of peptidoglycan biosynthesis, and atpH is an ATP synthase subunit. These studies demonstrate that a GWAS approach can be used to study the virulence of S. aureus by identifying potential regulators which can then be experimentally verified.
|Date of Award||11 Jul 2018|
|Supervisor||Ruth Massey (Supervisor)|