Lecture 27 and 28 Flashcards
Explain E. Coli features
-Gram negative
-Facultative anaerobe (can live without 02)
-Most strains are motile using flagella
pathogen 0157:h7
What happened in Walkerton?
- May 2000 contaminated the water supply for the town
- Contaminated farm run off entered groundwater reservoirs and wells
- Thousands sickened
- Now suffer from post infectious colitis
What are all those O numbers?
- There are over 700 antigenic types of E. coli
- Serotyping is done to distinguish which ones are associated with disease
-K number relates to capsular antigen
E. coli O157: [NM]
O antigen of LPS
Flagellar antigen
EHEC
- ingest cells to get an infection
- Primarily a disease of the developed world
- Not a common infection, but fatal and serious
- Extremely low infectious dose
- Zoonotic-from cattle
- Spread from animals to humans
- Can contaminate water supplies and vegetable crops
- Virulence determinants:pedestal formation and production of shiga toxin
What are the the type 3 secretion systems (T3SS sometimes TTSS)
- molecular syringe
- Related to flagellar apparatus
- For secretion of protein effectors directly into the host cells (as well as into extracellular milieu)
- Used by several important pathogens including Salmonella enterico, Shigella, Yersinia
What is secreton?
- It is a highly organized complex of many proteins
- Protein components of the secreton share homology with the flagellar basal body apparatus
Putting EHEC on a pedestal
-The T3SS of EHEC is used to inject a very peculiar effector into host cells: Tir (Translocated Intimin Receptor)
0Tir is inserted into the host cell membrane where it serves as a receptor for the bacterial adhesin, intimin
-Intimin (injects its own receptor in the host)
-The host recognizes Tir and modifies it, then inserts it into the host cell membrane
Steps to intimate attachment by EHEC #1
- The bacteria adhere to the surface of intestinal epithelial cells
- Adherence causes villi at the site of attachment to shrink (effece)
- Areas with attached bacteria look very different to healthy tissue
- Attaching/effacing or A/E lesions
- Pull them together close bc they repel each other bc of the overall negative charge
Steps to intimate attachment by EHEC #2
- TTSS expressed by attached bacteria
- Effector molecule Tir is injected into the host cells via TTSS
- Host recognizes Tir and places it into its cell membrane
- Bacterial surface protein, intimin, binds to Tir
- Initiates a cascade of signalling and cytoskeletal rearrangement to form a pedestal
Amazing architecture-what are effectors?
- Moves across the membrane-slides
- Tir is one of many effectors that are injected into the host cell
- Effectors are the mediators for communication between host and bacterium
Shiga toxin (Stx)
- Originally comes from a bacteriophage
- One of the most potent bacterial toxins known
- Acts to inhibit protein synthesis within target cells
- It is a ribotoxin
- Kidney cells are particularly sensitive to intoxication
2 subunits to this exotoxin-A and B (AB5)
-The b unit forms a pentamer in host cell and allows entry of the A active subunit
-E. coli 157 doesn’t cause disease in cattle bc the receptor for the toxin is absent
What is the difference between endotoxin and exotoxin?
Endotoxin
-component produced by gram negative bacteria
Contain lipid A which mammals are sensitive to.
What is retrograde trafficking?
-It is a way in which proteins and lipids are shuttled between endosomes and biosynthetic/secretory compartments such as the Golgi
Retrograde trafficking
- Stx binds to GB3 receptors on host cells
- Next is taken up by the host cell into an endosome
- Next is trafficked to the Golgi
- Then to the ER, where the active part of the toxin is separated from the binding part
- The active subunit enters the cytosol and injures ribosomes so that protein synthesis is halted
V. cholerae stats
- Proteobacteria (pathogen), related to E,coli
- Flagellated, highly motile bacterial cell (1 polar flagella), very short generation time
- Easy to grow
- Lives in salt and fresh water
- over 150 identified serotypes based on O antigen
- only 01 and O139 are toxigenic
