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12. E. coli Flashcards

1
Q

What diseases does E. coli cause?

A

Food poisoning, urinary tract infections

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2
Q

How does Escherichia coli cause disease?

A

T3SS, toxins, pathogenicity islands

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3
Q

Features of E. coli?

A
  • Gram negative
  • Rod-shaped
  • Motile
  • Commensal organism
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4
Q

What is E. coli involved in?

A

Diarrhoea, dysentery, HUS (hemolytic uremic syndrome), UTI, septicaemia, pneumonia, meningitis

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5
Q

What is a good illustration of the concept that it is the virulence factors which dictate the pathogenesis of an organism?

A

E. coli - not a ‘one disease’ organism

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6
Q

E. coli is differentiated based on?

A

Virotype/pathotype

based on virulence strategy and the disease caused rather than serotype

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7
Q

What are the different strains of E. coli?

A 
ETEC = enterotoxigenic E. coli
EPEC = enteropathogenic E. coli
EIEC = enteroinvasive E. coli
EHEC = enterohaemorrhagic E. coli
UPEC = uropathogenic E. coli
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8
Q

What causes ‘traveller’s diarrhoea’?

A

Enterotoxigenic E. coli (ETEC)

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9
Q

ETEC most resembles what in its pathogenesis?

A

V. cholerae - adheres to intestinal mucosa, produces toxin(s)

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10
Q

Symptoms of ETEC infection?

A

Watery diarrhoea, cramps, fever, malaise, usually self-limiting

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11
Q

True or False: A very high infectious dose of ETEC is necessary to establish colonisation of GIT

A

True (10⁸-10⁹)

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12
Q

Is there an effective vaccine for ETEC?

A

No

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13
Q

ETEC toxins?

A

Heat labile toxin (LT)
Heat stabile toxin (ST)
Both toxins are plasmid-linked

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14
Q

ETEC LT 75% identity with what toxin?

A

Cholera toxin (1 A, 5 identical Bs)

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15
Q

What does ETEC ST stimulate?

A

Guanylate cyclase to produce cGMP

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16
Q

What is responsible for paediatric/infantile diarrhoea?

A

Enteropathogenic E. coli (EPEC)

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17
Q

Death rate in third world countries among infants with EPEC infection?

A

50%, very low infectious dose in infants

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18
Q

Pathogenesis of EPEC?

A

Stage 1 - attaches to GIT, causes physical tissue damage

Stage 2 - effaces microvilli & forms a ‘pedestal’ on surface of cell

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19
Q

What part of EPEC encodes a T3SS?

A

LEE - locus for enterocyte effacement

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20
Q

What strain of E. coli causes bacillary dysentery?

A

Enteroinvasive E. coli (EIEC) - almost identical to Shigella in its pathogenesis & symptoms but does NOT produce Shiga toxin

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21
Q

Pathogenesis of EIEC?

A

Invade epithelial cells of small intestine

22
Q

What causes haemorrhagic colitis?

A

Enterohaemorrhagic E. coli (also called verotoxigenic E. coli)

23
Q

What particular serotype is normally associated with haemorrhagic colitis caused by EHEC?

A

O157:H7

Binds like EPEC, but then produces a toxin almost identical to Shiga toxin

24
Q

Symptoms of haemorrhagic colitis?

A

Severe cramps, very bloody diarrhoea

25
Long term complications associated with EHEC?
HUS (0-15% of patients) and TTP (thrombotic thrombocytopenic purpura, 50% fatality among elderly)
26
EHEC pathogenesis?
Infective dose very low (like Shigella) Appears to bind tightly to host cells (like EPEC) Produces vero-(Shiga)toxin
27
How are O157 unusual?
They are sorbitol negative (>95% of E. coli are positive)
28
What is EAEC?
Enteroaggregative E. coli - cause of acute and persistent diarrhoea
29
EAEC is defined by?
Its characteristic 'stacked brick' aggregative adherence when cultured with epithelial cells
30
What happens when EAEC adheres to the epithelium?
Enhanced epithelial mucus production - formation of a bacteria - mucus biofilm
31
What virulence plasmid in EAEC encodes factors required for adherence?
pAA
32
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
33
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
34
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
35
Where do most UPEC infections originate?
Colon
36
UPEC must be able to?
Colonise (adhere) & out-complete the vaginal microflora (usually lactobacilli)
37
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
38
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) ```
39
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 (UPEC)
40
What iron binding compounds does UPEC produce?
Siderophores
41
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)
42
How do we distinguish between strains of E. coli?
Serology - the antibodies they induce in the host 'O' anitgen (LPS) 'H' anitgen ( flagellar subunits)
43
How many possible serology combinations?
9,000
44
Is there a vaccine for E. coli?
No
45
What is HL Toxin?
- Heat Labile Toxin - Large peptides which can be degraded by heat - 100 degrees for 30 minutes lose activity - 75% identity with cholera - Complex A-B toxin & same mode of action and genetic organisation.
46
What is HS toxin?
- Small peptide (18 AA) excreted intracellular fluid - Stimulates guanylate cyclase to produce cGMP --> similar effect to increasing cAMP as achived by by LT and cholera toxin. - May mimic guanlyin, a peptide hormone
47
Who is EPEC associated with?
Bottle fed infants
48
What bacterium is EIEC almost identical to?
Shigella
49
What is EHEC also referred to as?
Verotoxigenic E. coli
50
What is the environment reservoir for EHEC?
Infects cattle - displays no symptoms
51
VTEC strain implicated with disease? How does it differentiate from O157:H7?
O104:H21

Microbiology (13 decks)

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