Characterisation of the role of two two-component signal transduction systems and a putative zinc metalloprotease in the virulence of Streptococcus pneumoniae
This thesis aimed to evaluate the contribution of several pneumococcal two-component systems to virulence by analysis of null mutants in a murine model of infection. In addition, a putative zinc metalloprotease, ZmpB, located immediately downstream of one of the TCS, was analysed for its role in virulence. Data indicated that one of the systems studied, TCS08, does not contribute significantly to virulence in serotype 2 pneumococcus, but may have a slightly more important role in a serotype 3 background. A second two-component system, TCS09, was found to be essential for virulence in a serotype 2. Despite the completely avirulent phenotype of the mutant, no difference in expression of many of the previously identified pneumococcal virulence-associated genes was detected in the mutant compared to its isogenic parental strain. Microarray analysis indicated that in serotype 2, TCS09 may be involved in nutrient perception in nutrient perception. TCS09 was found to be required for full virulence in a serotype 3 strain. In this strain, mutants appeared to be impaired in their ability to disseminate from the lungs to the blood in a pneumonia model of infection, but were not attenuated in virulence following direct inoculation into the systemic circulation. These data provide evidence that virulence determinants can behave differently based on the genetic background of the parental strain. ZmpB was found to contribute significantly to pneumococcal virulence in a serotype 3 strain. Further analysis of the contribution of this protein to infection found that ZmpB appears to have a role in promoting inflammation. Thus this work has identified ZmpB as being a novel pneumococcal virulence factor. The role of this protein in inflammation is being investigated further. This thesis has thus identified several genes important in the virulence of S. pneumoniae and work is currently ongoing to assess the potential of these genes as future vaccine or drug candidates. Data presented within this work also provides evidence that virulence determinants can behave differently based on the genetic background of the parent bacterial strain. This important observation could have significant implication for the future characterisation of pneumococcal virulence factors and may apply to other bacterial pathogens.