E.coli

Question 1

can be used as an indicator of

Answer 1

faecal pollution of water or poor hygienic status of some foods

Question 2

Characteristics such as Gram / shape / form spore?/ strain

Answer 2

Gram-negative rod-shaped bacterium
non-sporeforming
Most strains are completely harmless

Question 3

Found in

Answer 3

the intestines of warm-blooded animals as normal inhabitant

Question 4

Pathogenic E. coli types [5]

Answer 4

Enterotoxigenic (ETEC)
Enteroinvasive (EIEC)
Enterohaemorrhagic (EHEC)
Enteropathogenic (EPEC)
Enteroaggregative

Question 5

Enterotoxigenic (ETEC) symptom/ pathway/ serotype/ infectious dose

Answer 5

• leading cause of travellers’ diarrhoea and diarrhoea in developing countries
• cholera-like disease
• Profuse watery diarrhoea, low grade fever vomiting cramps, nausea
• Person-to-person spread (e.g. cruise ships)
• Associated with certain serotypes: 06,08, 015, 025, 063, 0125 etc.
• High infectious dose probably ~10^ 8

Question 6

Enteroinvasive (EIEC) symptom/ fermentation and by products / food source

Answer 6

• dysentery-like disease
• Profuse diarrhoea with high fever
• Blood and mucus in stools or dysentery-like symptoms

Organism resembles Shigella
Ferment lactose slowly or not at all, non-motile, no gas produced
Causes food poisoning only rarely (soft cheese Camembert, Brie)

Question 7

Enterohaemorrhagic (EHEC) symptom/ infectious dose

Answer 7

• Bloody diarrhoea (haemorrhagic colitis)
• Kidney damage (hemolytic uraemic syndrome, HUS)
• Brain damage (thrombotic thrombocytopaenic purpura, TPP)

Low infectious dose, ca. 10 cells, incubation period 1 to 4 days

Question 8

Enteropathogenic (EPEC) symptom

Answer 8

• somewhat similar to EHEC but less severe

- diarrhoea in nurseries in UK before 1950

Question 9

Enteroaggregative

Answer 9

• long lasting watery diarrhoea in children

- have fimbriae which aggregate tissue culture cells

Question 10

Disease causing mechanism of ETEC

Answer 10

• Attachment to gut epithelial cells via fibriae (pili)
• Injects protein toxins that interfere with fluid balance in the gut
• ST (heat stable toxin) causes cGMP accumulation in gut epithelial cells and subsequent secretion of fluid and electrolytes into the intestine
• LT (heat-labile toxin- similar to cholera toxin)

Question 11

Disease mechanism of EIEC

Answer 11

• Attach to gut epithelial cells using adhesin proteins
• Colonise large intestine, invade epithelial cells, cause ulceration
• No toxins but cause damage to cells
• Virulence plasmid codes for several outer membrane polypeptides involved in invasion

Question 12

Enterohaemorrhagic strains: E. coli O157 found in

Answer 12

Reservior in Intestines of healthy cattle and sheep

Isolations from 6% - 35% of cattle faecal samples in UK. Seasonal, highest in July

Question 13

E. coli O157 implicated in Foods such as

Answer 13

undercooked minced beef, cooked meats and pies, dry-cured salami, unpasteurised milk, unpasteurised apple juice, cheese , yoghurt, raw vegetables.

Question 14

E. coli O157 can be passed on by

Answer 14

Contact with animals:

children’s zoos/ camping, festivals

Question 15

EHEC Serotypes

Answer 15

O157:H7, O157 H-, O26, O103, O111, O113, O145

Question 16

VIRULENCE MECHANISMS OF EHEC

Answer 16

Verotoxigenic strains (VTEC) have one or more genes for verotoxin production VT1 VT2  (also called shiga-like toxins stx1 stx2)
But: many more genes needed for virulence
e.g. intimin gene eae (enterocyte effacement)

• Colonise colon
• Do not invade intestinal mucosa
• Cause ‘attaching and effacing lesions’
• Toxin depurinates residues on host cell ribosomes
• HUS in up to 10%; Mortality 1 to 5%

Question 17

Mechanisms for attachment and adhesionof E. coli O157:H7

Answer 17

Initial attachment (bundle-forming pili)

• -> [Signal transduction & Ca++ inositol phosphates] –>
• -> Formation of attaching and effacing lesion
• -> Insertion of translocated intimin receptor
• -> Intimate attachment and toxin production

Question 18

Tracing the source of an outbreak

Answer 18

Link was established with Pulsed Electric Field Gel Electrophoresis (PFGE).

• This method can identify a specific strain of a bacterium.
• Genomic DNA is digested with various restriction enzymes.
• Digested DNA fragments if identical will appear in the same position on the gel – similar band pattern.

Question 19

Diagnosis treatment OF E. coli O157:H7

Answer 19

• Culturing of the feces.
• dentification of the O and H antigens.
• Monitoring of renal function, blood hemoglobin platelets, administration of antimicrobial drugs.

Question 20

Prevention OF E. coli O157:H7

Answer 20

• Meat should be cooked thoroughly.
• Irradiation.
• Proper food handling.
• Water purification.
• Hygiene.
• Avoid consumption of local water and uncooked foods.

Question 21

Control measures: how do these compare with those available for Salmonella

Answer 21

Live animal:

Slaughter: minimise carcass contamination

New hygiene regulations in butchers’ shops (Pennington Report)

Food industry

Person to person: nursing homes

Control in the home

Contact with live animals: children’s zoos/ camping, water supplies etc

Question 22

Control measures for Live animal

Answer 22

no symptoms in cattle usually
no vaccine available
strict biosecurity not possible
feeding regimes may affect carriage (hay versus concentrates)
husbandry; dry bedding reduces incidence

Question 23

Control measures for Food industry

Answer 23

• HACCP
• pasteurise milk, including for cheese.
• 5D treatment for fruit juices (USA)

Question 24

Control measures for Control in the home

Answer 24

• cook burgers properly ‘until juice runs clear’ (70°C for 2 min)
• prevent cross contamination from raw to cooked food
• proper handling and chilled storage of cooked foods