What bacterium causes dysentery?

Shigella Species are the Primary Bacterial Cause of Dysentery

Dysentery is primarily caused by bacteria of the Shigella genus, including Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei. 1

Bacterial Pathogens Causing Dysentery

• Shigella species are the main bacterial cause of bacillary dysentery, characterized by frequent loose stools mixed with blood and mucus 2
• Four species of Shigella can cause dysentery:
  • Shigella dysenteriae (most severe, associated with complications) 3
  • Shigella flexneri (common in developing countries) 3
  • Shigella boydii 2
  • Shigella sonnei (predominant in industrialized countries, causes milder disease) 2

Clinical Presentation and Pathogenesis

• Shigellosis typically begins with watery diarrhea followed by dysentery with frequent mucoid bloody stools, abdominal cramps, and tenesmus 3
• Shigella bacteria invade the colonic mucosa, multiply within epithelial cells, cause cell death, and spread laterally to adjacent cells, resulting in mucosal ulceration, inflammation, and bleeding 3
• S. dysenteriae type 1 produces severe dysentery that may be associated with life-threatening complications including leukaemoid reaction and hemolytic-uremic syndrome 4

Diagnosis

• Laboratory diagnosis is made by culturing stool samples using selective/differential agar media 3
• When microscopy is available, stool specimens should be examined to identify the causative organism 1
• If microscopy is unavailable or trophozoites are not seen, persons with bloody diarrhea should be treated initially for shigellosis 1

Treatment Approach

• Antibiotics are the mainstay of therapy for all cases of shigellosis 4, 3
• Azithromycin should be considered the first-line agent in cases of dysentery due to increased likelihood of fluoroquinolone-resistant Campylobacter and other bacterial causes such as Shigella spp. 1
• Recommended azithromycin dosing: single 1-gm dose or 500 mg daily for 3 days 1
• Fluoroquinolones (ciprofloxacin) may be used to treat severe, non-dysenteric travelers' diarrhea but are less preferred for dysentery due to increasing resistance 1, 5
• Previously effective antibiotics like tetracycline, ampicillin, and co-trimoxazole have decreased efficacy due to antimicrobial resistance 4

Special Considerations

• Multidrug resistance is a serious problem in Shigella infections, particularly with S. dysenteriae type 1 2, 6
• Antimotility agents are contraindicated in dysentery 4
• Oral rehydration should be given concurrently to prevent or correct dehydration 4
• Hand-washing with soap and water helps prevent person-to-person transmission 4
• Currently, no vaccines against Shigella infection are available, though several candidates are under development 2, 3

Pitfalls and Caveats

• Shigella are highly fragile organisms, requiring careful collection and transport of stool specimens 3
• Amebic dysentery (caused by Entamoeba histolytica) can be misdiagnosed as shigellosis and requires different treatment 1
• Treatment for amebiasis should not be considered unless microscopic examination shows amebic trophozoites or two different antibiotics for shigellosis have not resulted in clinical improvement 1
• The global emergence of drug resistance limits antibiotic options, requiring awareness of local resistance patterns 3, 6