Shigella
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Bacteria - Gram Negative
- Neisseria spp: Overview
- Neisseria gonorrhoeae
- Neisseria meningitidis
- Haemophilus influenzae
- Bordetella pertussis
- Brucella
- Legionella pneumophila
- Pseudomonas aeruginosa: Overview
- Pseudomonas aeruginosa: Disease
- Salmonella Overview
- Salmonella typhi
- Salmonella enteritidis
- Shigella
- Yersinia enterocolitica
- Escherichia coli: Overview
- Enterohemorrhagic E. Coli (EHEC)
- Enterotoxigenic E. Coli (ETEC)
- Klebsiella pneumoniae
- Campylobacter jejuni
- Vibrio spp.
- Helicobacter pylori
- Borrelia burgdorferi (Lyme Disease)
- Leptospira interrogans
- Treponema pallidum: Overview
- Treponema pallidum: Diagnosis
- Congenital syphilis
- Chlamydia: Overview
- Chlamydia trachomatis
- Chlamydia pneumoniae vs. psittaci
- Rickettsia rickettsii
- Rickettsia typhi vs. prowazekii
- Anaplasma vs. Ehrlichia
- Coxiella burnetii (Q fever)
Shigella
- Includes S. sonnei, S. dysenteriae, S. boydii, and S. flexneri
- Characteristics
- Salmonella and Shigella spp. are all gram-negative rods, non-lactose fermenters, oxidase negative, and invade the GI tract via M cells of Peyer patches
- Gram-negative rod
- First test in algorithm, narrows scope of bacteria
- Does not ferment lactose
- Second test in algorithm
- Oxidase negative
- Third test in algorithm
- Does not produce H2S
- When grown on triple sugar iron agar
- Fourth test in algorithm, narrows to Shigella spp.
- Contrast w Salmonella spp. - H2S positive
- Non-motile (no flagella)
- Contrast w Salmonella spp. - motile
- Virulence factors
- Endotoxin
- Shiga toxin (enterotoxin)
- Inactivates 60S ribosomal subunit
- inhibits protein synthesis in intestinal cells
- E. coli’s shiga-like toxin (verotoxin) has the same structure, mechanism
- Toxin functionally plays a minor role in pathogenicity
- Inactivates 60S ribosomal subunit
- Transmission
- Reservoir is humans
- Fecal-oral (contaminated food or water)
- Especially undercooked meat
- More common in children
- Fecal-oral (contaminated food or water)
- Infectious dose (ID50) is low
- Acid-stable (resistant to gastric acid)
- requires only a small inoculum to invade and survive
- Contrast w Salmonella spp (acid labile, requires high infectious dose)
- Acid-stable (resistant to gastric acid)
- Reservoir is humans
- Pathogenesis
- Invades GI mucosa via M cells of Peyer patches
- M (microfold) cells make up lymphatic tissue that samples intestinal mucosa for antigens
- Escapes phagosomes and spreads cell-to-cell in mucosa
- no hematogenous spread (Contrast w Salmonella spp.)
- Causes ulceration and bleeding
- Direct bacterial spread is main cause of pathogenicity
- Not toxin-mediated damage (despite production of Shiga toxin)
- Invades GI mucosa via M cells of Peyer patches
- Presentation: Shigellosis
- GI manifestations
- Fever
- Crampy abdominal pain
- Bloody mucoid stools (bacillary dysentery)
- Contrast w Salmonella typhi - non-bloody diarrhea
- GI manifestations
- Treatment
- Supportive care (rehydration)
- Antibiotics in severe cases
- Ciprofloxacin, ceftriaxone, or TMP-SMX
- Zinc in young children shortens duration of disease and improves weight gain