Microbiology-C. Diff & Food Poisoning Flashcards
What is the single most common cause of acute gastroenteritis in the US?
Norovirus. It only needs a small dose to be infectious. It can be transmitted by food handlers and shellfish. Note that vomit is infectious.
What type of diarrhea do most viral gastroenteritis cases present with?
Watery
Describe the bacteria shown below.
This is clostridium, an anaerobic, spore-forming, gram positive rod
What are spores?
They are basically seeds that pop off the grown rod, land somewhere and germinate into another full cell.
What is the most frequently identified cause of nosocomial diarrhea?
C. difficile, this is triggered by prescribing antibiotics in a hospital setting. It is currently at historically high levels.
Most extreme form of c. difficile
The toxin enters the cell. Toxin B causes disaggregation of actin filaments by glucosylating RhoA, inactivating it, cells die and plaques form in the GI tract, causing pseudomembranous colitis.
How does C. difficile cause disease?
It is transmitted via the fecal oral route as a spore, which allows it to cross the acidic stomach. It germinates in the small intestine. In the large intestine it disrupts normal flora and produces enterotoxin A and necrotizing cytotoxin B. If there is no toxin, there is no disease. Some people get Clostridium Associated Diarrheal disease.
How do you treat someone who acquired C. difficile in the hospital?
Stop current antibiotic, give oral metronidazole and/or vancomycin. Fecal transplant is warranted for recurring illness.
A patient has been in the hospital for 4 weeks. Yesterday he presents with new onset abdominal cramps and diarrhea after being on antibiotics for the past week. Lab reveals leukocytosis. Sigmoid colonoscopy is shown below. How do you diagnose this patient with C. difficile?
Enzyme immunoassay for toxin A or toxin B in the stool. The gold standard is tissue culture cytotoxicity assay for toxin B. PCR molecular test works too.
What type of food poisoning is very common in Japan?
Vibrio parahemolyticus
What are the 3 main types of food borne illness?
1) Preformed toxins in food from clostridium botulinum, s. aueus and bacillus cereus 2) Intoxication caused by toxins made in the body from clostridium perfringens, ETEC or vibrio cholerae 3) Intestinal invades diseases like salmonella and campylobacter
Differentiate the mechanism of food borne illness, incubation period, reservoirs and clinical features in s. aureus, b. cereus, c. perfringens and salmonella/campylobacter.
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What type of food poisoning results in flaccid paralysis? What foods are risky?
Clostridium botulinum. Canned foods at an alkaline pH allows for spore germination.
On a commercial airline, 300 passengers got sick with nausea, vomiting, abdominal cramps and diarrhea. Epidemiological study reveals the cook as the source who had open lesions on his fingers. An lab studies reveal staph as the offending agent. How does staph cause food poisoning?
Staph aureus food poisoning happens as a result of toxin production that is a super antigen. Locking of the MHC II to the CD4 T cell causes massive release of IFN-gamma and TNF-alpha.
You go to a Chinese restaurant. You hate Chinese food, so all you eat is the rice. 2 hours later you have profuse vomiting. What is the likely cause of food poisoning?
B. cereus spore intoxication. Soaking of the rice allows for spore germination and food gets into your stomach as you eat the food.
