L13 E. coli

Question 1

What disease does E. coli cause?

Answer 1

Food poisoning, urinary tract infections

Question 2

How does Escherichia coli cause disease?

Answer 2

T3SS, toxins, pathogenicity islands

Question 3

Features of E. coli?

Answer 3

• Gram negative
• Rod-shaped
• Motile
• Commensal organism

Question 4

What is E. coli involved in?

Answer 4

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

Question 5

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

Answer 5

E. coli - not a ‘one disease’ organism

Question 6

E. coli is differentiated based on?

Answer 6

Virotype/pathotype (based on virulence strategy rather than serotype)

Question 7

What are the different strains of E. coli?

Answer 7

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

Question 8

What causes ‘traveller’s diarrhoea’?

Answer 8

Enterotoxigenic E. coli (ETEC)

Question 9

ETEC most resembles what in its pathogenesis?

Answer 9

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

Question 10

Symptoms of ETEC infection?

Answer 10

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

Question 11

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

Answer 11

True (10⁸-10⁹)

Question 12

Is there an effective vaccine for ETEC?

Answer 12

No

Question 13

ETEC toxins?

Answer 13

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

Question 14

ETEC LT 75% identity with what toxin?

Answer 14

Cholera toxin (1 A, 5 identical Bs)

Question 15

What does ETEC ST stimulate?

Answer 15

Guanylate cyclase to produce cGMP

Question 16

What is responsible for paediatric/infantile diarrhoea?

Answer 16

Enteropathogenic E. coli (EPEC)

Question 17

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

Answer 17

50%, very low infectious dose in infants

Question 18

Pathogenesis of EPEC?

Answer 18

Stage 1 - attaches to GIT, causes physical tissue damage

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

Question 19

What part of EPEC encodes a T3SS?

Answer 19

Locus for enterocyte effacement (LEE) pathogenicity island

Question 20

What strain of E. coli causes bacillary dysentery?

Answer 20

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

Question 21

Pathogenesis of EIEC?

Answer 21

Invade epithelial cells of small intestine

Question 22

What causes haemorrhagic colitis?

Answer 22

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

Question 23

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

Answer 23

O157:H7

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

Question 24

Symptoms of haemorrhagic colitis?

Answer 24

Severe cramps, very bloody diarrhoea

Question 25

Long term complications associated with EHEC?

Answer 25

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

Question 26

EHEC pathogenesis?

Answer 26

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

Question 27

How are O157 unusual?

Answer 27

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

Question 28

What is EAEC?

Answer 28

Enteroaggregative E. coli - cause of acute and persistent diarrhoea

Question 29

EAEC is defined by?

Answer 29

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

Question 30

What happens when EAEC adheres to the epithelium?

Answer 30

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

Question 31

What virulence plasmid in EAEC encodes factors required for adherence?

Answer 31

pAA

Question 32

What strain of E. coli is responsible for UTIs?

Answer 32

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

Question 33

UTI pathogenesis:

Answer 33

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

Question 34

Why are women more susceptible to UTIs than men?

Answer 34

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

Question 35

Where do most UPEC infections originate?

Answer 35

Colon

Question 36

UPEC must be able to?

Answer 36

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

Question 37

What is one of the principal host defences in UTI?

Answer 37

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

Question 38

Virulence factors UPEC?

Answer 38

Type 1 fimbriae (Fim) - most important in terms of cystitis 
P-pili - most important in terms of pyelonephritis
Afimbrial adhesins (AFAI, AFAIII, Dr adhesin)

Question 39

Haemolysins are important virulence factors. What are they?

Answer 39

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

Question 40

What iron binding compounds does UPEC produce?

Answer 40

Siderophores

Question 41

Treatment for UTI caused by UPEC?

Answer 41

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