Shigella spp.
One-Sentence Definition
Shigella species are non-motile, lactose-non-fermenting Enterobacterales that cause bacillary dysentery via intestinal invasion and Shiga toxin (some species) — low infectious dose and person-to-person spread.
Taxonomy & Morphology
- S. dysenteriae, S. flexneri, S. boydii, S. sonnei
- Gram-negative bacillus; non-lactose on MacConkey; closely related to Escherichia coli phylogenetically
Virulence Highlights
- M cell invasion; intercellular spread
- Shiga toxin (S. dysenteriae type 1) — HUS risk (similar mechanism to STEC)
- Very low inoculum — outbreaks in crowded settings
Clinical Syndromes
- Bloody diarrhea, cramps, fever (dysentery)
- Complications: dehydration, HUS (toxin-mediated), reactive arthritis
Diagnosis
- Stool culture on selective media; PCR on GI panels
- Distinguish from STEC — toxin testing and epidemiology
Treatment Notes (conceptual)
- Supportive hydration central
- Antibiotics shorten shedding in severe cases — resistance common; follow local guidelines
- Avoid antimotility agents in invasive diarrhea when possible
AMR Relevance
- MDR Shigella globally (fluoroquinolone, azithromycin resistance patterns vary)
Related Notes
- Escherichia coli (STEC) · Salmonella enterica · Gastrointestinal Infections
- MOCs: MOC - Bacteriology · MOC - Public Health & Epidemiology
Active Recall
- Why is person-to-person spread efficient?
- Shigella vs STEC — shared toxin concern?
- Lactose fermentation on MacConkey?