Screening of streptococcus pneumoniae ABC transporters for their role in virulence and investigation of their lipoprotein components as vaccine candidates

• Main Author: Basavanna, S.
• Published: University College London (University of London) 2011
• Subjects: 610
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.565522

Streptococcus pneumoniae causes life-threatening invasive diseases in children and older adults. Although effective at reducing the incidence of disease, the two currently available vaccines against S. pneumoniae have significant limitations that a vaccine based on protein antigens may overcome. For this thesis I have investigated the role of S. pneumoniae ABC transporters during infection, and have assessed as potential vaccine candidates the lipoprotein components of two ABC transporters. Eleven ABC transporters were chosen for investigation of their role during infection, and disruption mutant strains were successfully constructed for 9 of these. Two mutant strains disrupting the Sp0148-52 and Sp0749-53 ABC transporters, which BLAST searches suggest have methionine and branched chain amino acids (BCAAs) as substrates respectively, were markedly attenuated in systemic and pulmonary mice models of virulence. Western blotting and PCR confirmed that the lipoprotein components of these ABC transporters, Sp0149 and Sp0749, are present in all the S. pneumoniae strains investigated and are membrane-localised. Radioactive and fluorescence ligand binding experiments showed the Sp0749 lipoprotein specifically bound to BCAAs, confirming Sp0749-53 encodes a BCAA ABC transporter. Vaccination of mice with His6-Sp0149 and His6-Sp0749 induced specific IgG which was able to increase complement activity against and phagocytosis of S. pneumoniae. Intranasal immunisation of mice with His6-Sp0749 and His6-PiaA, affected the immune response to subsequent intranasal challenge with S. pneumoniae and increased lung inflammation upon subsequent S. pneumoniae intranasal challenge. However, both intraperitoneal and intranasal immunisation of mice with His6-Sp0149 and His6-Sp0749 resulted in only minor degrees of protection against S. pneumoniae septicaemia and pneumonia respectively. These results demonstrate that the S. pneumoniae BCAA ABC transporter is required for the full virulence, and its lipoprotein component can elicit immune responses against invasive S. pneumoniae that although weakly protective could contribute towards a multivalent vaccine.