Gram-negative, facultative anaerobic, nonspore forming, non-motile, rod-shaped bacteria closely related to Salmonella.
Causative agent of human shigellosis. During infection, it typically causes dysentery.
Shigella species are classified by four serogroups:
Serogroup A: S. dysenteriae (12 serotypes)
Serogroup B: S. flexneri (6 serotypes)
Serogroup C: S. boydii (18 serotypes)
Serogroup D: S. sonnei (1 serotype)
Groups A- C are physiologically similar; S. sonnei (group D) can be differentiated on the basis of biochemical metabolism assays.
Three Shigella 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.
Shigella infection is typically via ingestion (fecal-oral contamination); depending on age and condition of the host, fewer than 100 bacterial cells can be enough to cause an infection.
Shigella causes dysentery that results in the destruction of the epithelial cells of the intestinal mucosa in the cecum and rectum.
Some strains produce the enterotoxin shiga toxin, which is similar to the verotoxin of E. coli O157:H7 and other verotoxin-producing Escherichia coli. Both shiga toxin and verotoxin are associated with causing hemolytic uremic syndrome.
The most common symptoms are diarrhea, fever, nausea, vomiting, stomach cramps and flatulence. The stool may contain blood, mucus or pus.
Important considerations: The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions. Generally, the most common agents/regimens are listed first. Listed dosages may need to be adjusted for renal dysfunction.