L13 E. coli Flashcards
What disease does E. coli cause?
Food poisoning, urinary tract infections
How does Escherichia coli cause disease?
T3SS, toxins, pathogenicity islands
Features of E. coli?
- Gram negative
- Rod-shaped
- Motile
- Commensal organism
What is E. coli involved in?
Diarrhoea, dysentery, HUS (hemolytic uremic syndrome), UTI, septicaemia, pneumonia, meningitis
What is a good illustration of the concept that it is the virulence factors which dictate the pathogenesis of an organism?
E. coli - not a ‘one disease’ organism
E. coli is differentiated based on?
Virotype/pathotype (based on virulence strategy rather than serotype)
What are the different strains of E. coli?
ETEC = enterotoxigenic E. coli EPEC = enteropathogenic E. coli EIEC = enteroinvasive E. coli EHEC = enterohaemorrhagic E. coli UPEC = uropathogenic E. coli
What causes ‘traveller’s diarrhoea’?
Enterotoxigenic E. coli (ETEC)
ETEC most resembles what in its pathogenesis?
V. cholerae - adheres to intestinal mucosa, produces toxin(s)
Symptoms of ETEC infection?
Watery diarrhoea, cramps, fever, malaise, usually self-limiting
True or False: A very high infectious dose of ETEC is necessary to establish colonisation of GIT
True (10⁸-10⁹)
Is there an effective vaccine for ETEC?
No
ETEC toxins?
Heat labile toxin (LT)
Heat stabile toxin (ST)
Both toxins are plasmid-linked
ETEC LT 75% identity with what toxin?
Cholera toxin (1 A, 5 identical Bs)
What does ETEC ST stimulate?
Guanylate cyclase to produce cGMP
What is responsible for paediatric/infantile diarrhoea?
Enteropathogenic E. coli (EPEC)
Death rate in third world countries among infants with EPEC infection?
50%, very low infectious dose in infants
Pathogenesis of EPEC?
Stage 1 - attaches to GIT, causes physical tissue damage
Stage 2 - effaces microvilli & forms a ‘pedestal’ on surface of cell
What part of EPEC encodes a T3SS?
Locus for enterocyte effacement (LEE) pathogenicity island
What strain of E. coli causes bacillary dysentery?
Enteroinvasive E. coli (EIEC) - almost identical to Shigella in its pathogenesis & symptoms but does NOT produce Shiga toxin
Pathogenesis of EIEC?
Invade epithelial cells of small intestine
What causes haemorrhagic colitis?
Enterohaemorrhagic E. coli (also called verotoxigenic E. coli)
What particular serotype is normally associated with haemorrhagic colitis caused by EHEC?
O157:H7
Binds like EPEC, but then produces a toxin almost identical to Shiga toxin
Symptoms of haemorrhagic colitis?
Severe cramps, very bloody diarrhoea
Long term complications associated with EHEC?
HUS (0-15% of patients) and TTP (thrombotic thrombocytopenic purpura, 50% fatality among elderly)
EHEC pathogenesis?
Infective dose very low (like Shigella)
Appears to bind tightly to host cells (like EPEC)
Produces vero-(Shiga)toxin
How are O157 unusual?
They are sorbitol negative (>95% of E. coli are positive)
What is EAEC?
Enteroaggregative E. coli - cause of acute and persistent diarrhoea
EAEC is defined by?
Its characteristic ‘stacked brick’ aggregative adherence when cultured with epithelial cells
What happens when EAEC adheres to the epithelium?
Enhanced epithelial mucus production - formation of a bacteria - mucus biofilm
What virulence plasmid in EAEC encodes factors required for adherence?
pAA
What strain of E. coli is responsible for UTIs?
Uropathogenic E. coli (UPEC) - most infections involve females of <10 years & between 20 and 40 yrs
UTI pathogenesis:
Almost always ascending infections
Severity depends on the site of infection:
1. Urethritis (urethra) - burning sensation during urination
2. Cystitis (bladder) - burning sensation during urination
3. Pyelonephritis (kidney) - back pain & fever
Why are women more susceptible to UTIs than men?
Physically easier for contamination between GIT and urethra - a woman’s urinary tract more likely to get infected than a man’s
Where do most UPEC infections originate?
Colon
UPEC must be able to?
Colonise (adhere) & out-complete the vaginal microflora (usually lactobacilli)
What is one of the principal host defences in UTI?
The washing action of urine - the bacteria must adhere in order to not be diluted out
Virulence factors UPEC?
Type 1 fimbriae (Fim) - most important in terms of cystitis P-pili - most important in terms of pyelonephritis Afimbrial adhesins (AFAI, AFAIII, Dr adhesin)
Haemolysins are important virulence factors. What are they?
These are pore-forming exotoxins, which can lead to cell damage in the kidneys - may be an attempt to acquire iron
What iron binding compounds does UPEC produce?
Siderophores
Treatment for UTI caused by UPEC?
Oral antibiotics, drink large amounts of liquid to aid flushing action. Nosocomial (hospital acquired) pyelonephritis may require more aggressive treatment (IV antibiotics)
