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24 Cards in this Set

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Salmonella and Shigella are two important Gram neg bacteria that cause enterocolitis. How are they differentiated?
Shigella and Salmonella both ferment lactose. However, Salmonella produces gas from glucose fermentation, produces H2S and is motile.
Which is more infective, Salmonella or Shigella?
Less than 10 organisms are required for Shigella to cause infection because it is very resistant to stomach acid. Salmonella is not as resistant and requires 10 6X to 10 9X organisms to cause disease.
What other bacteria besides Shigella contain the Shiga toxin?
The hemorrhagic and invasive strains of E coli.
What are the mechanisms of the two subunits of Shiga toxin?
Subunit A. Inhibits 60S ribosome, stopping protein synthesis, killing the intestinal cell.
What is the function of of Subunit B regarding the Shiga toxin?
It helps subunit A enter cells by binding to the microvillus membrane in the large intestine.
What are the reservoirs for Shigella?
Only humans, there are no animal carriers.
What symptoms are often seen with Shigellosis?
Bloody diarrhea, fever and lower abdominal cramps.
How is Shigella transmitted?
Four F's. Fingers, food, flies and feces.
What populations are most often affected by Shigella?
Nursing home residents and very young children(ages 2-4) especially those in developing countries.
Whatb is the treatment for Shigella and what medications should be avoided?
Treatment includes fluid/electrolyte replacement and antibiotics such as TMP-SMX and ciprofloxacin. Antidiarrheals such as Immodium should be avoided, as they may prolong and worsen illness.
Why does Shigella only cause superficial ulcers and not invade blood vessels?
Once Shigella enters M cells in the intestine, it uses actin trails to travel among cells without entering the extracellular matrix. Thus , Shigella remains within epithelial intestinal cells, causing ulcers.
Salmonella species are divided into typhoidal and non-typhoidal types. Describe the diseases caused by each and the species included in each.
Typhoidal: Salmonella typhii and Salmonella paratyphoidal causes typhoid fever.
Nontyphoidal: Salmonella enteriditidis and salmonella cholerasuis cause enterocolitis, osteomyelitis and Septicemia.
How do typhoidal strains differ from nontyphoidal strains of Salmonella in terms of reservoirs?
S. typhi and S. paratyphi have only human reservoirs, while nontyphoidal strains have both human and animal reservoirs(chikens and turtles)
What makes S. typhi resistant to macrophage killing?
Inhibits phago-lysosome fusion and defensins resist O2 dependent and independent killing.
Where does infection with S. typhi begin and where does it spread to?
S. typhi begins in the ileoceccal intestines and spreads hematogenously and through the lymphatic system to the liver, bone marrow, gallbladder and spleen.
What organ harbors S. typhi in a chronic carrier state?
Gallbladder
What cells in particular harbor S. typhi and facilitate its dissemination?
Monocytes, those in Peyer's patches in the ileocecal intestines are the initial target.
Typhoid fever is a protracted disease of about 3 weeks. Describe the pathogenesis and symptoms seen each week.
1. Bacteremia with fever/chills
2. Monocyte involvement with organ inflammation, abdominal pain and rash.
3. Ulceration of Peyers patches, intestinal bleeding and shock.
Sescribe the location and appearance of the rash seen in week 2?
Rose spots, small transient, pink rash located on the abdomen(seen in 30% of patients).
What is the appropriate therapy for S. typhi infection?
Ciprofloxacin, ceftriaxone or azithromycin.
What disease is typhoid fever often mistaken for? Why?
Appendicitis, patients present with right lower quadrant abdominal pain without rash.
How does non typhoidal Salmonella cause enterocolitis and describe the type of diarrhea?
Salmonella directly invades epithelial cells of the small and large intestines. Presents with fever and bloody diarrhea with inflammatory white blood cells(similar to EIEC).
How do you treat Salmonella enterocolitis?
Supportive therapy. It resolves in about a week.
What patients are at increased risk for Salmonella osteomyelitis?
Sickle cells disease patients due to autosplenectomy.