- Most common cause of bloody Diarrhea in the United States (since 2010 when surpassed E. coli 0157:H7)
- Characteristics
- Facultative Anaerobic Gram Negative Rod in Enterobacteriaceae family
- Grouped with SS Gram Negative Bacteria (Salmonella, Shigella)
- Humans are the only hosts for Shigella
- Shigella is not a normal colonizer of the human intestinal tract (always pathogenic)
- Distinguished from other Enterobacteriaceae
- Non-motile as it has no flagella (unlike E. coli, Enterobacter, Serratia, Salmonella, Citrobacter and Proteus)
- Does not ferment lactose (unlike E. coli)
- Does not produce Hydrogen Sulfide or H2S (unlike Salmonella)
- Facultative Anaerobic Gram Negative Rod in Enterobacteriaceae family
- Mechanism of Toxicity
- Only small inoculum required for infection
- Invades Small Bowel mucosa
- Produces Enterotoxin (Shiga Toxin) in colon
- Similar to the Enterotoxin in Enteroinvasive E. coli and Enterohemorrhagic E. coli
- Two different Enterotoxins have been identified (ShET-1, ShET-2)
- A Subunit (Active)
- Deactivates 60S ribosome (at 28S rRNA)
- Inhibits Protein synthesis, thereby killing intestinal epithelial cells
- B Subunit (Binding)
- Five B subunits are attached to each A subunit
- B Subunits bind colon's microvillus membrane (at Glycolipid Gb3 receptor)
- Toxin results in exaggerated inflammatory response, resulting in colitis and dysentary
- Epithelial cells are sloughed off, leaving shallow ulcerations
- Fluid losses are related to intestinal cell injury, unable to reabsorb fluid and Electrolytes
- Transmission
- Occurs via items contaminated with human feces (Hand contact, Fly infestation)
- Foodborne Sources (fecal-oral route)
- Contaminated drinking water
- Contaminated raw produce
- Foods contaminated by infected food handler
- Sexually Transmitted Infection (anal sex)
- More common among Men who have Sex with Men
- Four serotypes
- Shigella sonnei
- Most common Shigella species causing Infectious Diarrhea in industrialized countries
- Shigella flexneri
- Most common Shigella species causing Infectious Diarrhea in tropical and subtropical regions
- Growing Incidence as a Sexually Transmitted Infection in the United States
- Associated with anal sex and oro-anal sex, and presents with severe Diarrhea
- Multi-drug resistant and treatment requires susceptibility testing
- Associated with HIV Infection
- Shigella dysenteriae
- Less common outside of South Asia and Sub-Saharian Africa
- Shigella boydii
- Less common outside of South Asia and Sub-Saharian Africa
- Shigella sonnei
- Foodborne Sources (fecal-oral route)
- Preschool children
- Nursing Home residents
- Sexually Transmitted Infection (anal sex)
- Fever (58% of cases)
- Dehydration
- Lower abdominal tenderness
- Hyperemic bowel wall
- Mural edema
- Purulent exudate
-
Stool microscopy
- Stool Mucus
- Fecal Leukocytes present
- Complete Blood Count
- Routine Stool Culture
- Negative only after 48 hours of Antibiotics
- See Acute Diarrhea
- Treat Immunocompromised patients for 7-10 days
- Trimethoprim-Sulfamethoxazole (Bactrim) is no longer recommended due to Antibiotic Resistance
- Adults with Dysentery: first-line agents
- Ciprofloxacin 500 mg orally twice daily for 3 days or
- Levofloxacin 500-750 mg orally daily for 3 days
- Adults with Dysentery: alternative agents
- Azithromycin 500 mg daily for 3 days or
- Ceftriaxone 1-2 g IV daily for 3 days (in severe disease)
- Children with Dysentery: first-line agents
- Azithromycin 10 mg/kg/day daily for 3 days or
- Ceftriaxone 50-75 mg/kg/day for 2- 5 days (in severe disease)
- References
- (2015) Sanford Guide to Antimicrobial Therapy, IOS app accessed 5/8/2016
- CDC Shigella