- Aerobic Gram-negative rod (Fig), non-motile, non-spore-forming), family Enterobacteriaceae.
- Four groups: subdivided into serotypes and subserotypes based upon lipopolysaccharide O antigenic repeats.
- Group A (S. dysenteriae, see separate module for discussion of Group A infections, often cause of pandemics arising from natural and man-made disasters)
- Group B (S. flexneri, leading cause in low- and middle-income countries)
- Group C (S. boydii, relatively uncommon cause)
- Group D (S. sonnei, the leading diarrhea cause in high-income countries)
- >46 serotypes mean low protective immunity develops when exposed to new infections to prevent the next.
- In clinical microbiology laboratories, MacConkey or EMB agar yields the best growth in addition to Shigella-Salmonella agar.
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