Type IV O antigen modification genes in the genome of Shigella flexneri NCTC 8296

The genes encoding type IV O antigen glucosylation were characterized from both Escherichia coli and Shigella flexneri. The putative O antigen modific ation genes from E. coli, o120 o306 o443, were PCR-amplified and introduced into S. flexneri serotype Y strain SFL124. Immunogold labelling and phage sensitivity indicated the presence of both serotype Y and serotype 4a O ant igens on the cell surface of the resulting recombinant SFL124 strains, sugg esting that only partial serotype conversion was conferred by the E. coli g enes. The type IV O antigen modification genes were then isolated and chara cterized from S. flexneri serotype 4a strain NCTC 8296. A 3.8 kb chromosoma l fragment conferred complete conversion to serotype 4a when introduced int o SFL124. Sequence analysis of the fragment revealed the presence of three genes, gtrA(IV) gtrB(IV) gtrIV(Sf). DNAs homologous to bacteriophage int an d attP were located upstream of gtrA(IV), suggesting that this region of th e NCTC 8296 genome may have originated from a bacteriophage; however, a ser otype-converting phage could not be induced from this strain nor from of he r strains used in this study. Comparison of the GtrIV(Sf) and GtrIV(Ec) (o4 43) proteins revealed that they are 41% identical and 63% similar, which is the highest degree of similarity reported among the S. flexneri O antigen glucosyltransferases.