Micro Exam 3- part 5
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What are the common normal flora found in the large and small intestines?
Helicobacter pylori- gram and shape?
Curved gram negative rod
What are the virulence mechanisms associated with H. pylori?
- Motile (flagella)
- Urease (neutralizes stomach acid)
- vacA (encodes for a cytotoxin- induces vacuoles)
- cagA (cytotoxin associated gene, increase virulence)
- Induce inflammation
Which two diseases is H. pylori implicated in?
- Chronic gastritis
- Gastric and duodenal ulcers
How is EPEC transmitted?
Contaminated food and water
What are the virulence mechanisms of EPEC?
- -Attachment via bundle-forming pili
- -Type III secretion system
- -Intimate contact with enterocyte via intimin
- -Actin recruitment via activated tyrosine kinase
- -Deformation of microvilli and pedestal formation
How is EPEC diagnosed in the lab?
Lactose positive on MacConkey Agar
How is Shigella often transmitted?
- Oral-fecal route
- Contaminated water or food
Shigella- gram and shape?
Gram negative bacilli
Which serogroup of Shigella causes the most infections in the U.S.?
S. sonnei (Group D)
What are the virulence mechanisms of Shigella?
- -Invasion- type II secretion system
- -Toxin production (S. dysenteriae)
- -Attaches to enterocyte or M cell
- -Taken up by the cell, transcytoses through the cell, phagocytosed by macrophages
- -Macrophages release IL-1 and IL-8, causes influx of PMNs and inflammation
- -Intracellular spread via actin rearrangement
How is Shigella diagnosed in the lab?
What is the clinical manifestation of Shigella?
Which bacteria produce Shiga toxin?
E coli O157:H7 and Shigella dysenteriae
How is EHEC transmitted?
- Contaminated food or water (usually beef)
- Person to person (oral-fecal)
What are the O and H indicative of in E. coli O157:H7?
- O= antigen serotype
- H= flagellar serotype
What is the mechanism of action of the Shiga toxin (or Shiga-like toxin)?
- AB toxin
- -Binds to Gb3 receptor on host cell (highest concentration in renal tissue)
- -Cleaves 28s ribosome
- -Prevents protein synthesis
What are the clinical manifestations of EHEC?
- Hemolytic Uremic Syndome (acute renal failure, thrombocytopenia, hemoyltic anemia)
What are the culture characteristics of EHEC?
- Lactose positive
- Sorbitol negative
Vibrio cholerae- gram and shape?
Curved gram negative bacilli
What is a serogroup?
Same species with different antigenic determinants on cell surface
What is a biotype?
Same species with different physiological or biochemical traits
What is the virulence mechanism of V. cholerae?
- Cholera toxin
- -AB toin
- -A subunit ADP riboslates Gs protein--> increase levels of cAMP --> activate CFTR --> efflux of ions and water
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