E.coli Flashcards
can be used as an indicator of
faecal pollution of water or poor hygienic status of some foods
Characteristics such as Gram / shape / form spore?/ strain
Gram-negative rod-shaped bacterium
non-sporeforming
Most strains are completely harmless
Found in
the intestines of warm-blooded animals as normal inhabitant
Pathogenic E. coli types [5]
Enterotoxigenic (ETEC) Enteroinvasive (EIEC) Enterohaemorrhagic (EHEC) Enteropathogenic (EPEC) Enteroaggregative
Enterotoxigenic (ETEC) symptom/ pathway/ serotype/ infectious dose
- 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
Enteroinvasive (EIEC) symptom/ fermentation and by products / food source
- 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)
Enterohaemorrhagic (EHEC) symptom/ infectious dose
- 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
Enteropathogenic (EPEC) symptom
- somewhat similar to EHEC but less severe
- diarrhoea in nurseries in UK before 1950
Enteroaggregative
- long lasting watery diarrhoea in children
- have fimbriae which aggregate tissue culture cells
Disease causing mechanism of ETEC
- 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)
Disease mechanism of EIEC
- 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
Enterohaemorrhagic strains: E. coli O157 found in
Reservior in Intestines of healthy cattle and sheep
Isolations from 6% - 35% of cattle faecal samples in UK. Seasonal, highest in July
E. coli O157 implicated in Foods such as
undercooked minced beef, cooked meats and pies, dry-cured salami, unpasteurised milk, unpasteurised apple juice, cheese , yoghurt, raw vegetables.
E. coli O157 can be passed on by
Contact with animals:
children’s zoos/ camping, festivals
EHEC Serotypes
O157:H7, O157 H-, O26, O103, O111, O113, O145
VIRULENCE MECHANISMS OF EHEC
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%
Mechanisms for attachment and adhesionof E. coli O157:H7
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
Tracing the source of an outbreak
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.
Diagnosis treatment OF E. coli O157:H7
- Culturing of the feces.
- dentification of the O and H antigens.
- Monitoring of renal function, blood hemoglobin platelets, administration of antimicrobial drugs.
Prevention OF E. coli O157:H7
- Meat should be cooked thoroughly.
- Irradiation.
- Proper food handling.
- Water purification.
- Hygiene.
- Avoid consumption of local water and uncooked foods.
Control measures: how do these compare with those available for Salmonella
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
Control measures for Live animal
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
Control measures for Food industry
- HACCP
- pasteurise milk, including for cheese.
- 5D treatment for fruit juices (USA)
Control measures for Control in the home
- 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
