The four species of Shigella are:
*Shigella sonnei (the most common species in the United States)
*Shigella flexneri
*Shigella boydii
*Shigella dysenteriae
Shigella dysentery was the first associated enteric infection to be recognized. S. dysenteriae type 1 (not commonly present in the US, except in travelers returning from endemic areas) produces Shiga toxin, which causes marked watery diarrhea and sometimes hemolytic-uremic syndrome.
S. dysenteriae type 1 is the causative agent of the most severe form of bacillary dysentery, which occurs as epidemics in many developing countries. S. dysenteriae type 1 produces a potent cytotoxin (Shiga toxin) that causes local destruction of colonic epithelium, so disease due to this strain is more severe and prolonged than that produced by other species.
S. dysenteriae is a gram-negative bacterium that causes bacillary dysentery or shigellosis. S. dysenteriae spread by contaminated water and food, causes the most severe disease because of its potent exotoxin.
The disease can be divided into two phases.
*First phase: occurring in the first 1 to 2 days, consists of watery diarrhea and cramping; this phase is mediated by an enterotoxin. Process involves:
- Ingestion
- Noninvasive colonization and cell multiplication
- Production of the enterotoxin by the pathogenic bacteria in the small intestine
*Second phase: is caused by invasion of the organism into the large intestine and produces fever, cramps, bloody diarrhea, and tenesmus.
Shigella dysenteriae
