6.2 pathogenicity islands Flashcards
(20 cards)
how is E.coli helpful
it aids in digestion, produces vitamins B12 and K, and protects intestinal tract from bacterial infections
how is E. coli harmful
foreign DNA has been transferred into E. coli, bringing genes that encode proteins that have turned this good bacterium into a pathogen
pathogenic Escherichia coli – all pathogenic strains are..
intestinal parasites, and a few produce potent enterotoxins
examples of patogenic strains of E. coli
shiga toxin-producing E. coli or STEC, also known as E. coli O157:H7
pathogenicity islands
- arose from horizontal gene transfer
- encodes genes that contribute to virulence of the pathogen
- are incorporated into the genome of the pathogenic bacteria
virulence factors of E. coli O157:H7
- pathogenic Island (LEE)
- Shiga Toxins
- Plasmid O157
two surface components of E. coli form the basis for the serological classification system - what are they
O antigen of LPS (O), and H antigen of flagella (H)
O antigen of LPS
acts as water soluble carriers for the toxic Lipid A – gene for the O157 antigen was transferred into E. coli on a plasmid and is expressed in the LPS – alters virulence
H antigen
consists of proteins that form the filament of the flagellum – many modifications of this protein exist – presenting diff flavour of antigen.
what does LEE stand for
the Locus of Enterocyte Effacement
LEE description
– this PAI is associated with intestinal cell attachment and diarrheal disease.
– Encodes secreted proteins, a secretion system, regulators to control the genes within the PAI
– STEC E. coli inserts its own receptor into intestinal cell mem for cellular attachment
comparison of flagellum and type III secretion system
lacks motor therefore does not spin
– has all other structural elements that enable anchoring in the cell membrane, a channel to pass through periplasma space, and ability to shunt cargo into extracellular environment
translocation of STEC-secreted proteins steps
- STEC uses pili to attach to the membrane of eneterocyte
- activates its type III S.S
- third step of infection is characterized by enterocyte effacement (thinning of membrane, pedestal formation, intimate bacterial attachment to host cell)
- its type III S.S appartus - a filamentous translocation tube - transport proteins from bacterial cell to host cell
- Tir is transported to host cell and inserts itself into host cell membrane
intimate attachment to host cell requires outer bacterial membrane protein called
intamin
STEC mediates pedestal formation – steps
– bacterial cell has produced a lot of intamin and Tir
- Tir has been shunted out of bacterial cell through type III S.S and has been inserted on host cell membrane
- Tir acts as a receptor for intamin
- actin starbs building chain which stabilizes the pedestal
- the bacteria stays attached to the host cell holding on tightly.
Shiga toxin is secreted by STEC – what happens when it is secreted
when shiga toxin is secreted – gets into bloodstream where destroys red blood cells
– generates a condition that can occur when the small blood vessels in your kidney become damaged/inflamed
– causes clots to form leads to kidney failure
Shiga toxin mechanism of action
- AB5 from bloodstream binds to glycolipid receptor (Gb3) pn endothelial cell and is then internalized
- the vesicle the AB5 toxin is now in fuses with the golgi, and is trafficked to the ER
- at ER, A1 subunit is released and binds to 60S ribosome
- this causes protein synthesis in the host cell to cease, and cell death follows.
E. coli produce ___ fibres
curli
what do curli fibres do
enhance biofilm formation
How does the bovine intestinal epithelium differ from human – what does this mean infection wise
STEC colonizes this surface, but it is not toxic in cattle.
– this is because the preferred receptor for the shiga toxin, Gb3, is not expressed on bovine epithelial cells
– this means that while cows carry STEC, the shiga toxin is ineffective – cows show NO SIGN of infection
– why we can get infected by eating raw meat
- also cow manure is used for fertilization therefore can obtain infection from leafy greens
