Structure of the Shigella dysenteriae 7 O antigen gene cluster and identification of its antigen specific genes.

Shigella strains are human pathogens. The O antigen gene cluster of Shigella dysenteriae O7 was sequenced and analyzed. It contains genes for synthesis of nucleotide sugars including UDP-2-acetamido-2-deoxy-D-galacturonamide, UDP-2-acetamido-2-deoxy-D-galacturonic acid and dTDP-4-amino-4,6-dideoxy-D-glucose. Also found in the gene cluster are genes encoding O unit flippase, O antigen polymerase and sugar transferases. The Escherichia coli O121 O antigen, which is present in an important Shiga toxin-producing strain, has the same structure as that of S. dysenteriae O7, and we found that the gene clusters also had the same genes and organization. Four genes specific to S. dysenteriae O7 and E. coli O121 were identified by PCR screening against representatives of 186 E. coli (including Shigella) O serotypes. E. coli O121 and S. dysenteriae O7 isolates can be distinguished by PCR of the H antigen fliC gene.