Molecular basis of O-antigen modification and genomics of serotype-converting bacteriophages of Shigella flexneri

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There are approximately 165 million cases of shigellosis world wide annually, resulting in 1.1 million deaths. The majority of cases occur in developing countries and most deaths occur in children under 5 years of age. Shigellosis is mainly caused by the bacterium Shigella flexneri. There are 13 different serotypes of S. flexneri determined by bacterial cell-surface polysaccharides called O-antigens. Bacterial viruses (bacteriophages) carry the genes which confer O-antigen variation. Infection and subsequent incorporation of the virus into the genetic material of the bacterial cell result in modification of the bacterial O-antigen. This phage-mediated O-antigen modification gives rise to different serotypes. The project will address fundamental processes related to the O-antigen modification. This will be achieved by studying structure and function of the enzymes encoded by the O-antigen modification gene cluster. We have isolated several serotype-converting bacteriophages from S. flexneri and we plan to compare and characterise their genomic information to increase understanding of their origin and relationship with the bacterial host.