Micriobiology of the GIT Flashcards
Pathogens common to the small intestine.
- Cholera, ETEC/EPEC, Staph. aureus, Giardia
Pathogens common to the large intestine.
- Salmonella, Campylobacter, C. dificile, EHEC/EIEC
What are the 4 main pathogenic strains of E. coli in relation to the intestinal tract? How does each cause damage?
- entero-toxigenic (ETEC): enterotoxins (heat labile and heat stable types); small bowel; traveler’s diarrhea; non-inflammatory
- entero-pathogenic (EPEC): adherence (no toxins); small bowel; diarrhea in children
- entero-hemorrhagic (EHEC): O157:H7; shiga-like toxin (AKA STEC); hemolytic-uremic syndrome; large bowel; dysentery
- entero-invasive (EIEC): invasion; large bowel; dysentery
Which pathogenic E. coli strains are most important in terms of the global incidence of diarrhea? What about of developed countries?
- global: ETEC (50% of traveler’s diarrhea) and EPEC
- developed countries: EHEC
What is the most common cause of food-associated diarrhea in the 1st world?
- salmonella, EXCEPT for the U.S. and U.K. where it is campylobacter
Most cases of Salmonella are self-limiting, but which two strains are often invasive and cause a much more severe illness?
- S. typhi and S. paratyphi
- they cause Typhoid Fever by invading the Peyer’s patches
Which pathogen is most commonly associated with poultry?
- campylobacter! NOT salmonella
- (88% of birds are infected with some pathogen; 63% w/ campylobacter, 16% with salmonella, and 8% with both)
Why are Campylobacter infections quite common?
- because their infective dose is very low
About 1 in every 1000 patients infected with Campylobacter develop which syndrome?
- Guillain-Barre syndrome; inflammation of the peripheral nerves resulting in ascending paralysis
Which organism causes Cholera? Where is it commonly found? What type of classic diarrhea results?
- Vibrio cholerae
- found in endemic S.E. Asia, parts of Africa, and S. America
- patients have massive amounts of rice water stool diarrhea
Shigellosis is primarily a disease of what age group? Which animals are reservoirs of shigella?
- children
- the only reservoirs are humans and primates!
What is the most common cause of diarrhea in infants? In children?
- infants: viral infection (norovirus and rotovirus)
- children: ETEC and EPEC
Which organisms do we fight with antiobiotics?
- Campylobacter, Shigella, C. dificile, and Typhoid
Food poisoning is NOT the same as food borne infection; which 3 traits make up food poisoning? Which 2 organisms are commonly involved?
- ingestion of preformed toxins, treated with antitoxin, and does NOT usually involve diarrhea
- S. aureus and C. botulinum
The major organism involved in Esophagitis is __________. Two other main causes are _______ and _______.
- major organism: Candida albicans
- other causes: HSV-1 and CMV
Pathogens involved in non-inflammatory gastroenteritis.
- Staph aureus, Bacillus cereus, ETEC, Vibrio cholerae, Clostridium botulinum, Clostridium perfringens, rotavirus, norovirus, Giardia lamblia
- (large overlap with pathogens affecting the small intestine)
Pathogens involved in inflammatory gastroenteritis.
- Campylobacter jejuni, Salmonella, Shigella, EPEC, EHEC, EIEC, Clostridium difficile
Pathogens involved in penetrating enteric infection (which is similar to inflammatory enteritis, but worse).
- Typhoid/enteric fever via Salmonella typhi and Salmonella paratyphi
- Yersinia enterocolitica
Staphylococcus aureus
- Gram positive cocci; clusters
- due to human contamination of food
- usually infects small bowel; non-inflammatory
- the S. auerus toxin (TSST) is a super antigen that is heat, trypsin, and pepsin stable and can cause toxic shock syndrome
- food poisoning is due to ingestion of preformed toxin
Bacillus cerreus
- Gram positive rod; aerobic organism; spores
- due to unrefrigerated “left out” food, reheated rice
- non-inflammatory
- 2 types of toxins; type I (rice): vomiting; type II (meat and cream): diarrhea and some vomiting
Clostridium
- Gram positive rod; obligate ANaerobic organism; spores
- usually infect the large bowel
- due to reheated meat (C. perfringens) and improperly canned foods (C. botulinum); these are non-inflammatory
- due to antibiotics (C. dificile); inflammatory
Vibrio cholerae
- Gram negative rod; comma shaped highly motile
- usually infects the small bowel; non-inflammatory
- due to human fecal-oral contact; contaminated water
- endemic to developing countries
- massive quantity of rice water stool
Describe the enterotoxin involved in Cholera.
- it’s an A-B subunit structure
- A: involved in the permanent ADP-ribosylation (inactivation) of GTP-binding protein of Gs, resulting in a permanent increase in cAMP levels = excess secretion
- B: binding domain to the host cell
Campylobacter jejuni
- Gram negative rod; curved (comma or S shaped)
- usually infects the large bowel; inflammatory
- due to contaminated milk, water, undercooked poultry
- common cause of Guillain-Barre syndrome
Salmonella
- Gram negative rod; aerobic organism; flagella
- usually infects the large bowel; inflammatory
- due to contaminated food of animal origin (many animal reservoirs)
What is Hemolytic-Uremic Syndrome? Which organism can cause it?
- a triad of anemia, thrombocytopenia, and acute renal failure
- associated with the shiga-like toxin produced by EHEC/STEC
- damaged areas from the toxin develop microthrombi, resulting in mechanical hemolysis (anemia) and decreased renal blood flow; the microthrombi consume platelets = thrombocytopenia
Mumps Virus
- a paramyxovirus
- causes parotitis (parotids), orchitis (testes), and aseptic meningitis
- sterility is therefore a potential complication
- can also cause acute pancreatitis
- “mumps makes your parotids as big as POM-poms”
What type of virus is each hepatitis virus?
- HAV: RNA picornavirus
- HBV: DNA hepadnavirus
- HCV: RNA flavivirus
- HDV: RNA delta virus
- HEV: RNA hepvirus
aHAV (IgM), aHAV (IgG), HBsAg, aHBs, HBcAg, aHBc, HBeAg, aHBe
- aHAV (IgM): best test to detect active HAV virus
- aHAV (IgG): indicates prior HAV infection and/or prior vaccination; protects against reinfection
- HBsAg: indicates HBV infection
- aHBs: indicates immunity to HBV
- HBcAg: antigen of the core of HBV
- aHBc (IgM): acute/recent infection of HBV
- aHBc (IgG): prior exposure to or chronic infection of HBV
- HBeAg: indicates active viral replication and high transmissibility
- aHBe: indicates low transmissibility
- (aHBc and aHBe will be present during the window period)
Helicobacter pylori
- Gram negative rod; curved
- catalse, oxidase, and urease positive
- diagnose with urea breath test (because H. pylori converts urea to ammonia and CO2; patient ingests radio-labelled urea –> if radio-labelled CO2 is exhaled, the test is positive)
- causes gastritis and PUD; creates an alkaline environment for survival
- it is strictly a human reservoir!
Virulence Factors of H. pylori
- catalase, SOD, urease, mucinase, Vac-A (cytotoxin, responsible for ulceration), Cag-A (reprograms infected cells to create a nicer environment, associated with increased risk of gastric cancer)
