Vaccine development against the infectious killer, Clostridium difficile

Clostridium difficile is the leading cause of health care-associated infections worldwide. In the United States alone, the CDC estimated almost half a million Clostridium difficile infections (CDI) in 2011 with 29,000 deaths within 30 days of diagnosis. The elevating incidence of CDI across the globe, the emerging antibiotic resistance of this organism and the lack of available prophylactics urgently call for the development of an effective vaccine.

In the past, conventional strategies to develop vaccines capable of eliciting serum bactericidal antibody responses that protect against bacterial disease has been time consuming (up to 15 years). Moreover these traditional approaches can only identify and exploit antigens that are highly expressed and immunogenic during disease. In more recent years, with the increasing availability of whole genome sequences, in silico approaches have been used to make predictions about putative antigens that are localised to the cell surface and conserved between diverse strains. These vaccine candidates can then be tested in vivo for their ability to induce serum bactericidal antibody responses and their ability to protect against infection. Reverse vaccinology is not only fast (approximately 2 years) but thorough, allowing the identification of all potential antigens, irrespective of their level of expression, time of expression or immunogenicity and can be applied to all pathogens.

This project sets out to use PSORT-B and other predictive algorithms to identify putative vaccine antigens from the genome sequence of C. difficile strain 630. The conservancy of these antigens will be tested by BLASTp analysis against all available partial and complete genome sequences of this organism as well as by PCR and sequencing of non-sequenced strains. The genes encoding conserved antigens will be cloned into an Escherichia coli expression vector and the antigens subsequently purified by Immobilized Metal Affinity Chromatography. Their immunogenicity will be tested in the hamster model for C. difficile infection. Briefly after immunisation with the antigens, sera will be harvested and reactivity to the panel of antigens tested by Western blotting and bactericidal activity tested in in vitro assays. The most promising of these antigens will be further investigated for their ability to protect from C. difficile infection by challenge experiments with spores in the hamster model.

This 3.5-year PhD project is funded by the School of Life Sciences at the University of Nottingham which works in close association with the Biomedical Research Centre (BRC) funded by the National Institute for Health Research (NIHR). This project will be conducted in the Clostridia Research Group (CRG) headed by Professor Nigel Minton. The CRG is part of the £14.3 M BBSRC/EPSRC Synthetic Biology Research Centre (SBRC – www.sbrc-nottingham.ac.uk) which boasts state-of-the-art facilities within the Centre for Biomolecular Sciences. These facilities include a £1.1M Beckman Robotic workstation and 11 twin occupancy anaerobic cabinets.