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Microbiology > 12. E. coli > Flashcards

12. E. coli Flashcards

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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
Q

Long term complications associated with EHEC?

A

HUS (0-15% of patients) and TTP (thrombotic thrombocytopenic purpura, 50% fatality among elderly)

26
Q

EHEC pathogenesis?

A

Infective dose very low (like Shigella)
Appears to bind tightly to host cells (like EPEC)
Produces vero-(Shiga)toxin

27
Q

How are O157 unusual?

A

They are sorbitol negative (>95% of E. coli are positive)

28
Q

What is EAEC?

A

Enteroaggregative E. coli - cause of acute and persistent diarrhoea

29
Q

EAEC is defined by?

A

Its characteristic ‘stacked brick’ aggregative adherence when cultured with epithelial cells

30
Q

What happens when EAEC adheres to the epithelium?

A

Enhanced epithelial mucus production - formation of a bacteria - mucus biofilm

31
Q

What virulence plasmid in EAEC encodes factors required for adherence?

A

pAA

32
Q

What strain of E. coli is responsible for UTIs?

A

Uropathogenic E. coli (UPEC) - most infections involve females of <10 years & between 20 and 40 yrs

33
Q

UTI pathogenesis:

A

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
Q

Why are women more susceptible to UTIs than men?

A

Physically easier for contamination between GIT and urethra - a woman’s urinary tract more likely to get infected than a man’s

35
Q

Where do most UPEC infections originate?

A

Colon

36
Q

UPEC must be able to?

A

Colonise (adhere) & out-complete the vaginal microflora (usually lactobacilli)

37
Q

What is one of the principal host defences in UTI?

A

The washing action of urine - the bacteria must adhere in order to not be diluted out

38
Q

Virulence factors UPEC?

A 
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
Q

Haemolysins are important virulence factors. What are they?

A

These are pore-forming exotoxins, which can lead to cell damage in the kidneys - may be an attempt to acquire iron
(UPEC)

40
Q

What iron binding compounds does UPEC produce?

A

Siderophores

41
Q

Treatment for UTI caused by UPEC?

A

Oral antibiotics, drink large amounts of liquid to aid flushing action. Nosocomial (hospital acquired) pyelonephritis may require more aggressive treatment (IV antibiotics)

42
Q

How do we distinguish between strains of E. coli?

A

Serology - the antibodies they induce in the host
‘O’ anitgen (LPS)
‘H’ anitgen ( flagellar subunits)

43
Q

How many possible serology combinations?

A

9,000

44
Q

Is there a vaccine for E. coli?

A

No

45
Q

What is HL Toxin?

A
  • 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
Q

What is HS toxin?

A
  • 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
Q

Who is EPEC associated with?

A

Bottle fed infants

48
Q

What bacterium is EIEC almost identical to?

A

Shigella

49
Q

What is EHEC also referred to as?

A

Verotoxigenic E. coli

50
Q

What is the environment reservoir for EHEC?

A

Infects cattle - displays no symptoms

51
Q

VTEC strain implicated with disease? How does it differentiate from O157:H7?

A

O104:H21

Microbiology (13 decks)

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