<unk>  species are classified by three serogroups and one serotype: * Serogroup A: S. dysenteriae (15 serotypes) * Serogroup B: S. flexneri (9 serotypes) * Serogroup C: S. boydii (19 serotypes) * Serogroup D: S. sonnei (one serotype) Groups A–C are physiologically similar; S. sonnei (group D) can be differentiated on the basis of biochemical metabolism assays. Three<unk>  groups are the major disease-causing species: S. flexneri is the most frequently isolated species worldwide, and accounts for 60% of cases in the developing world; S. sonnei causes 77% of cases in the developed world, compared to only 15% of cases in the developing world; and S. dysenteriae is usually the cause of epidemics of dysentery, particularly in confined populations such as refugee camps. Each of the<unk>  genomes includes a virulence plasmid that encodes conserved primary virulence determinants. The<unk>  chromosomes share most of their genes with those of E. coli K12 strain MG1655. Phylogenetic studies indicate<unk>  is more appropriately treated as subgenus of Escherichia, and that certain strains generally considered E. coli—such as E. coli O157:H7—are better placed in<unk>  (see Escherichia coli#Diversity for details).
Shigella
Salmonella
Giardia
Vibrio cholerae
Faecalibacterium
Clostridioides difficile 
Escherichia coli
Campylobacter jejuni