
It is a member of the Enterobacteriaceae family. It is a gram negative, non-motile, non-sporeless, non-encapsulated, facultative anaerobic, oxidative and fermentative metabolism bacillus that is pathogenic for humans. Bacteria of the genus Shigella (O) are divided into groups as A, B, C, D according to their somatic antigen structures and their effects on mannitol. These groups are; S. dysenteriae, S. flexneri, S. boydii, S. sonnei.
Mannit Negative Shigella s S. dysenteriae (Serogroup A)
Serovar A1 (S. dysenteriae = Shiga bacillus)
Serovar A2 (S. schmitzii)
Serovars A3-7 (in S. arabinotar)
Serovars A8-12
Mannit Positive Shigella s S. flexneri (Serogroup B, serovars; B 1-6,X, Y)
S. boydii (Serogroup C, serovar; C 1-18)
S. sonnei (Serogroup D, serovar; D)
Although Shigella are immobile, movement is seen only in Shigella flexneri with Type-1 fimbria. Shigella are distinguished from Salmonella by being inactive. They make bacteriocin (colisine), which acts on other gut bacteria. When the bacteria is lysed, the somatic antigen (O) is released, which is in lipoprotein structure and has endotoxin properties. Of the Shigella, only Shigella dysenteriae secretes exotoxin to the environment. Shigellas cause edema, profuse mucus secretion, abscesses and ulcerations in the large intestinal mucosal epithelium. While these bacteria can survive for a long time in watery, moist and sunless environments, they are not resistant to high heat, sunlight and antiseptics.