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Title: Evolutionary and ecological considerations of social behaviours in Staphylococcus aureus
Author: Pollitt, Eric Joseph Gabriel
ISNI:       0000 0004 6351 376X
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2014
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The growth and virulence of the major human pathogen Staphylococcus aureus, is dependent upon a cell-to-cell signalling mechanism known as quorum sensing (QS). QS co­ordinates the production of virulence factors at a group level via the production and sensing of autoinducing peptide (AIP) signal molecules by the agr locus. Here, the role and social nature of QS is examined in 1) a virulence model using waxmoth larvae and 2] a motility model whereby S. aureus colonies expand on soft agar surfaces. Infection of waxmoth larvae showed that 1) QS in S. aureus is a cooperative social trait, which provides a benefit to cells at the group or population level; 2] wild-type cells are exploited by agr mutants, which act as social cheats within the group and invade wild-type populations; 3) the presence of agr cheats results in reduced virulence during infection and 4) population diversity but not transmission rate affects whether QS is maintained. These results provide a possible explanation as to why agr mutants show reduced virulence in animal models but can be isolated from infections of humans. qqr-dependentQS also controls spreading motility, which has been previously described as a passive form of motility. Here it is shown that S. aureus is capable of a form of active motility called gliding, and thatS. aureus can move as 'comets’ of cells that are encased in a matrix. As S. aureus is generally believed to be non- motile, this discovery may provide new insights into how S. aureus survives in the environment and during infection. Finally, an investigation into S. aureus phenotypic and antibiotic susceptibility diversity from a single clinical sample was performed. S. aureus colonies isolated from a case of bacteraemia associated with a gluteal abscess revealed no variation in antibiotic susceptibility or growth yield in the population. Overall, research in this thesis provides new insights into social behaviours regulated by qqr-dependent QS in 5. aureus and demonstrates for the first time that QS is social in S. aureus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available