Bacterial Diarrhea Flashcards
Shigella
- one of the most highly infectious enteric pathogens worldwide*
- only takes 200 units to cause disease
Always produces dysentery
- watery diarrhea (sometimes bloody)
- fever
- extreme stomachache
Sole reservoirs is humans and primates
Highest incidence is in children = 1-4 yrs
Characteristics:
- Gram (-) rod
- nonspore-former
- facultative intracellular anaerobe
- nonmotile
- lactase (-)*
4 species of shigella
A = most severe; D = less severe
A = S. Dysenteriae
B = S. Flexneri
C = S. Boydii
D = S. Sonnei
in US, B and D are the most common by far
Shigella pathogenesis
Enteric bacilli enters the epithelial cells which induces inflammatory Disease of the large bowel
- occurs within 72 hrs after exposure
Initial symptoms:
- Watery diarrhea
- fever
- cramps
- vomiting
Progressive symptoms:
- bloody/mucous/PMN in stool
- fever
- Cramps
- Tenesmus (cramping severe rectal pain (also feels like you need to constantly use the bathroom))
Shigella virulence factors
Enterotoxins
1) Pic = cleaves mucus membranes (allows for better entrench into epithelial cells)
2) SigA = induces severe cytotoxicity
3) SepA = unknown
4) Surface O LPS = induces endocytosis into M cells unwillingly
5) actin binding (comet tails)
- similar to listeria
6) shiga toxin = inhibits 60s ribosomes in cells which causes apoptosis and Autophagy of infected cells. Also promotes inflammation
Hemolytic uremic syndrome (HUS)
very common in untreated S. dysenteriae infections, but can be any of them
Shiga toxin gets into kidneys and induces apoptosis of kidney cells = acute kidney failure
also can be provoked by antibiotic therapy (since shiga toxin is mass released due to death of shigella bacteria), so need to monitor
Reiter’s syndrome/reactive arthrtis related to shigella
Strong association with shigella plasma-antigens
Often can induce this so need to monitor for it
What is the #1 prevention for shigella?
Hand washing
Vibrio cholerae
Produces massive watery diarrhea and prolonged hypersecretion of electrolytes
- this severe dehydration kills often
Incubation = 12 hrs- 3 days
Presentation:
- acute onset nausea and vomiting
- then profuse watery diarrhea
Characteristics:
- gram (-) comma-shaped
- motile
- grows on TCBS agar* (produces yellow colonies)
Vibrio cholerae pathogenesis
Cholera toxin
- CtxA/CtxB
- heat liable enterotoxin
- CtxA = triggers efflux of ions and water into lumen (reverses receptors)
- upregulated cAMP as well as reverses receptors
How to treat cholera besides antibiotics
Rehydration therapy (focus on electrolytes) - dont overload with water
- Zinc treatment has shown to help improve in children*
- acts to stop upregulation cAMP and allow water and electrolytes to stay in rather than move out
C. Diff
Is an enterotoxic gram (+) spore former
- obligate anaerobes
- catalase (-)
- oxidase (-)
- motile*
- produces saprophytes*
- *Causes pseudomembranous colits**
- very commonly associated with previous systemic antibiotic (ampicillin/clindamycin/fluroquinolones) therapies (kills good bacteria)
Presentation:
- diarrhea (watery/bloody)
- cramps
- fever
- leukocytosis
What toxins does antibiotic resistant C. Diff produce?
Toxin A: enterotoxin that produces diarrhea
Toxin B: cytotoxin that kills cells and also produces diarrhea
Clostridium perfringens
A part of the clostridium family that isnt as common in GI as C. Dif, but can still present
- *always presents WITHOUT fever and NO pseudomembranes
enterotoxins: are heat-liable that results in hypersecretion
Exotoxins: alpha toxin
- degrades tissues and cell membranes
- myonecrosis leads to gas gangrene
- also double zone of hemolysis on blood agar
Campylobacter jejuni
Intracellular commensal bacteria
- found in birds and mammals and common infect due to contaminated dairy/poultry products
Produces intestinal and systemic infections in human
Characteristics:
- “gull-winged”/spiral shaped gram (-) rods
- microaerophilic
- grow on macconkey agar
- **specific skirrow agar grows ONLY campylobacter jejuni
- oxidase (+)
- catalase (+/-)
What is the most prevalent bacteria isolated from enteric infections?
C. Jejuni
