S. flexneri is subtyped into various serotypes based on the combination(s) of antigenic determinants present in the O-antigen. Structural studies have shown that all S. flexneri O-antigens, except for serotype 6, are polymers of the basic tetrasaccharide repeating unit, which is found in S. flexneri serotype Y strains. Addition of a glucosyl, O-acetyl or phosphoethanolamine residue to the basic O-antigen results in serotype conversion (O-antigen modification). My group is investigating the genetic basis of the emergence and diversity of S. flexneri serotypes.
The factors involved in several O-antigen modifications have been identified and characterised from different bacteriophages in my laboratory. We are studying the molecular biology of these bacteriophages to understand their origin, evolution and interactions with the bacterial host. My group is also attempting to unravel the fundamental issues pertaining to the O-antigen modification. We are investigating how different transferases involved in O-antigen modifications function in the bacterial membrane and determine serotype specificity in S. flexneri. While serotype-conversion is essential in generating antigenic variation, little is known about its role in virulence. Using genetic and functional approaches, we are examining the effect that it has on the virulence characteristics of S. flexneri.