Structural and genetic evidence that the Escherichia coli O148 O antigen is the precursor of the Shigella dysenteriae type 1 O antigen and identification of a glucosyltransferase gene

摘要

Shigella dysenteriae type 1 is the most virulent serotype of Shigella.Enterotoxigenic Escherichia coli O148 is pathogenic and can cause diarrhoea.The following structure was established for the tetrasaccharide repeating unit of the E.coli O148 O antigen: ->3)-alpha-L-Rhap-(1->3)-alpha-L-Rhap-(1->2)-alpha-D-Glcp-(1->3)-alpha-D-GlcpNAc-(1->.This differs from the structure reported earlier for S.dysenteriae type 1 by having a glucose (Glc) residue in place of a galactose (Gal) residue.The two bacteria also have the same genes for O antigen synthesis,with the same organization and high level of DNA identity,except that in S.dysenteriae type 1 wbbG is interrupted by a deletion,and a galactosyltransferase gene wbbP located on a plasmid is responsible for the transfer of galactose to make a novel antigenic epitope of the O antigen.The S.dysenteriae type 1 O antigen was reconstructed by replacing the E.coli O 148 wbbG gene with the wbbP gene,and it had the LPS structure and antigenic properties of S.dysenteriae type 1,indicating that the S.dysenteriae type 1 O antigen evolved from that of E.coli O 148.It was also confirmed that wbbG of E.coli O 148 is a glucosyltransferase gene,and two serotype-specific genes of E.coli O148 and S.dysenteriae type 1 were identified.