Proteomic investigation of the group B streptococcus

Yang, Qian (2011) Proteomic investigation of the group B streptococcus. Doctoral thesis, Northumbria University.

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Abstract

The Group B Streptococcus (GBS) is a Gram-positive opportunistic pathogen which is a leading cause of neonatal disease globally. In 2000-2001, the general incidence of neonatal GBS infection was 0.72 per 1000 live births in U.K. and the mortality rate is about 10%, because of which neonatal GBS disease is a significant burden on society. GBS is part of the commensal flora, colonising the vagina and gastrointestinal tract of women. Vertical transmission is the main cause of early onset GBS disease. During the process of GBS neonatal disease, GBS must be able to survive in several very different host environments, including the vagina, amniotic fluid, the neonate?s lung and blood. The vagina is normally acidic, low oxygen and with limited nutrients while the neonate?s lung and blood are neutral, high oxygen and with abundant nutrient. Proteomic investigations of GBS protein expression under conditions representing those associated with benign maternal colonisation and foetal exposure may help us understand the molecular basis of GBS virulence. GBS growth characteristics, long term survival, acid adaptation, viable but non-culturable state and biofilm formation were investigated to help us understand how GBS survives in different environments and also help us to develop an in vitro model to reflect in vivo conditions during GBS disease development. An in vitro model of GBS growth under conditions reflecting maternal vaginal carriage (low pH, low oxygen, nutrient stress) and exposure to body fluids during invasive disease (neutral pH, aeration, nutrient sufficient) was established. Proteins expressed under each growth conditions were separated by two dimensional electrophoresis. Individual proteins were subjected to in-gel trypsin digestion and identified using liquid chromatography-mass spectrometry with peptide mass fingerprinting followed with bioinformatic research. A total of 76 proteins were identified and 16 of these were expressed differentially. The putative virulence factor C protein ? antigen and proteins involved in responses to oxidative stress were up-regulated under the conditions reflecting neonatal exposure. Another in vitro model of GBS growth on Todd Hewitt agar in the presence or absence of 10% human serum was established and followed by proteomic investigation of proteins differentially expressed under these two conditions, as this model reflects GBS neonatal septicaemia (exposure to serum). A total of 84 proteins were identified and 11 of which were expressed differentially. The putative virulence factor C protein ? antigen, arginine deiminase, an ABC transporter substrate-binding protein and glyceraldehyde-3-phosphate dehydrogenase were up-regulated in the presence of human serum.

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