The differentiation between subspecies, and the phylogenetic position of clones within clones was determined by analysis of restriction fragment length polymorphisms of rDNA (ribotyping). Seventy-five strains belonging to the four subspecies and 13 enteroinvasive (EIEC) strains were compared with the 72 strains of the ECOR collection, which have been classified into four phylogenetic groups (A, B1, B2 and D). Seventeen Shigella dysenteriae ribotypes, 12 Shigella flexneri ribotypes, 23 Shigella boydii ribotypes, 12 ribotypes and 13 EIEC ribotypes were identified following digestion with and Correspondence analysis of the data showed that serotype 13 strains were distantly related to the other strains, and that and were distinct from and The ribotypes of Shigella and ECOR strains were indistinguishable, and and most strains were closely related to phylogenetic group D, whereas serotype 1 strains belonged to phylogenetic group B1, and strains were evenly distributed between the two groups. The strains were distantly related to group B2, which contains strains frequently implicated in extra-intestinal infections in humans. In contrast, the 13 EIEC strains were more widely distributed between phylogenetic groups B1, A and B2. Thus, there was no primordial species and and EIEC strains are derived from different ancestral strains.


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