Staphylococcus aureus virulence gene studies : a comparative microarray based approach

Mohamed, Deqa Hassan A. (2010). Staphylococcus aureus virulence gene studies : a comparative microarray based approach. PhD thesis The Open University.



The development and application of a partial composite S. aureus virulence-associated gene micro array is described. Epidemic, pandemic and sporadic lineages of healthcare associated(HA-) and community-associated (CA-) S. aureus were compared. The clonal population structure was supported but further evidence for large-scale recombination events was obtained. Phage structural genes linked with the CA phenotype were identified and in silico analysis revealed these to be correlated with phage serogroup. CA strains generally carried a PVL-associated phage either of the A or Fb serogroup, whilst the HA strains predominantly carried sero group B phage. It is proposed that carriage of PVL associated phage rather than the specific pvl genes is correlated with the CA phenotype.These findings further support the role of the accessory genome in shaping the epidemiology of S. aureus.

The microarray was used to study gene expression in isogenic strains differing by a deletion in the agr locus. Microarray analysis revealed significant differences between the levels of expression of several genes of the normal and mutant strains. However, RNAIII levels in the non-mutant strain were found to be cell density independent, indicating that the expected quorum sensing mechanism was not functional.

Expression profiles of cells grown under biofilm simulating conditions were compared to their planktonic counterparts. Biofilm cells displayed a typical expression profile that was different from both the actively growing planktonic exponential cells and the planktonic stationary cells. The strongest feature of the biofilm state was high level expression of the haemolysin genes. This model therefore is amenable to exploitation in studies designed to improve our understanding of the mechanisms underlining biofilm survival and regulation after long periods of growth.

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