Cell-surface antigens and virulence factors of Escherichia coli O157

Shiga toxin-producing Escherichia coli (STEC) strains are commensal bacteria in cattle with high potential for transmission to humans. The serotype E. coli O157:H7 is the main cause of hemorrhagic colitis and hemolytic-uremic syndrome. E. coli O157 synthesizes an O-antigen containing a repeating tetrasaccharide with the structure (4-N-acetyl-perosamine -> 3-fucose -> 3-glucose -> 3-N-acetyl-galactosmine). The presence of a common epitope consisting of 2-substituted N-acyl-perosamine is responsible for the serological crossreactions with Yersinia enterocolitica O9 or Vibrio cholerae O1. The sequence homology indicates that the 0157:H7 rfbE gene encoding perosamine synthetase may have originated in a species other than E. coli. The peculiarity of 0157 repeat unit biosynthesis is a new pathway performed by epimerase Gnu that catalyses the reversible epimerization of N-acetyl-glucosamine-P-P-undecaprenol to N-acetyl-galactosmine-P-P-undecaprenol. The potential of the bacterial epimerase as a new target for antimicrobial agents is discussed. O157 and H7 antigens seem to be accessory virulence factors implicated in the pathogenesis of human diseases. The O157 antigen is important in the animal and plant host immune response and plays a role in the adherence of this organism to epithelial cells. One of the sources of epidemic outbreaks is water from the municipal water supply and other reservoirs. Survival of O157 bacteria in water environments has been recorded. The comparative analysis of nucleotide sequences within the rfb O antigen gene cluster and of other genes in the genome among STEC strains will elucidate the genetic basis of the evolution and virulence of these enteric pathogens.