Genetic regulation of virulence in Streptococcus pneumoniae

Herbert, Jenny (2012) Genetic regulation of virulence in Streptococcus pneumoniae. PhD thesis, University of Glasgow.

Abstract

S.pneumoniae is the leading cause of bacterial pneumonia and meningitis. Pneumonia alone has been estimated to kill more children under the age of five than that caused by AIDS, malaria and tuberculosis combined. The current vaccines which are used to prevent pneumococcal infection only protect against a small number of the 90+ serotypes currently identified. Current issues which may prevent the long term use of these vaccines is capsular switching, a phenomenon observed where some strains are able to escape the vaccine through switching their capsule genes. Further serotype replacement has been shown to occur since the introduction of the PCV7 vaccine, where serotypes not protected against by the vaccine have caused a higher incidence of invasive pneumococcal disease compared to the pre vaccine era. One strategy to avoid this is via the use of a multi-component protein based vaccine which is serotype independent.

The pneumococcus is normally found as a harmless commensal yet can also cause invasive disease as stated above, the pneumococcus is also the leading cause of otitis media. The ability for the pathogen to occupy a number of different niches and evade host defences is attributed to its large cache of virulence factors, including numerous cell surface adhesins. The ability of the bacteria to regulate genes required for adaptation to a specified niche is vital for survival. In this study a number of signalling systems that are able to modulate gene expression (specifically virulence factors) to facilitate adaptation to varying environmental conditions are assessed to determine the genes they regulate. Further key environmental signals are evaluated to determine the effect they have on regulation of important cell surface adhesins.

The main systems used to modulate global expression changes are two-component signal transduction systems (TCS). 13 TCS and one orphan response regulator are encoded in the pneumococcal genome. Little information is available with regards to the importance of each system, whether each system regulates its own separate collection of genes and the extent to which cross regulation may occur between these systems. This study used whole genome expression analysis data obtained through microarray analysis of single and double TCS mutants to assess the potential cross regulation of two chosen systems. A number of the systems have also been shown to regulate the same islet, which encodes a pilus. Measuring expression of the islet itself enabled the role of the systems shown to regulate the islet to be assessed for potential interactions between the systems and whether a hierarchy exists.

The pneumococcus is highly genetically variable due to its ability to become naturally competent, taking up DNA from the environment and recombining it into its genomic DNA to aid genetic variation and survival. The new era of whole genome sequencing has begun to shed light on just how variable this pathogen is. Although a number of TCS have been shown to regulate pilus expression, with the use of whole genome sequencing of two closely related strains (one contains reduced pili expression levels) a number of other factors have also been identified which have been shown to alter pilus expression, this includes a serine/ threonine protein kinase, pyruvate oxidase and lactate oxidase. Further the pneumococcus has been shown to respond to exogenously added hydrogen peroxide which increases pilus expression levels. Levels of hydrogen peroxide may act as a key environmental cue to signal to the bacterium that they are present in the nasopharynx and require increased levels of cell surface adhesins.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Pneumococcus, two-component signal transduction, pilus, virulence, adhesin
• Subjects: Q Science > QR Microbiology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Infection & Immunity > Bacteriology
• Supervisor's Name: Mitchell, Prof. Timothy J.
• Date of Award: 2012
• Depositing User: Dr Jenny A Herbert
• Unique ID: glathesis:2012-4204
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 25 Apr 2013 11:37
• Last Modified: 04 Jul 2016 10:40
• URI: https://theses.gla.ac.uk/id/eprint/4204