E. coli and Diarrhoea

Infectious diarrhoea
1. 3-5 billion episodes each year
2. Major cause of worldwide morbidity and mortality
  1. Major cause of absence from work/schoool
    1. Major economic burden - especially in developing countries
3. 5 million deaths each year - 80% <1 y.o.
4. 80% foodborne diarrhoea caused by bacteria
5. Organisms
  1. Parasites - Giardia, Amoeba, Ascaris etc.
  2. Viruses - Noravirus, Rotavirus, Cytomegalovirus (CMV) etc.
  3. Bacteria - E. coli, Salmonella, Shigella, Campylobacter, Vibrio, Yersinia, C. difficile, S. aureus, B. cereus, C. botulinum
  4. Mechanisms of causing diarrhoea
    1. Osmotic
    2. Secretory
    3. Exudation
    4. Abnormal motility
6. Syndromes
  1. Food poisoning
  2. Acute watery diarrhoea - Traveller's diarrhoea/epidemics
  3. Acute bloody diarrhoea - dysentry
7. Special circumstances
  1. Outbreaks/food poisoning
  2. Overseas travel
  3. Immunocompromised host
  4. Raw seafood ingestion
  5. Antibiotic usage
98% of daily intake and endogenous solutions is absorbed in intestine
Osmotic Diarrhoea
1. Increased amounts of poorly absorbed, osmotically active solutes in gut lumen
  1. Solutes act as laxatives
2. Interferes with water absorption
3. Solutes are ingested (fasting stops diarrhoea)
  1. Magnesium sulphate/citrate/magnesium containing antacids
  2. Sorbitol
  3. Malabsorption of food
Secretory Diarrhoea
1. Excess secretion of electrolytes and water across mucosal surface
2. Usually coupled with inhibition of absorption
3. Very large and watery stools
4. Fasting doesn't stop diarrhoea
5. Stimuli
  1. Mucosal/Submucosal
    1. Prostaglandins/Leukotrines
    2. Cytokines
    3. Reactive oxygen metabolites
    4. Platelet activating factor
  2. Blood Hormone
    1. Serotonin (carcinoid)
    2. Vasoactive intestinal peptide (WDHA)
    3. Calcitonin (medullary carcinoma of thyroid)
  3. Luminal
    1. Enterotoxins
    2. Bile salts
    3. OH-fatty acids
  4. Bacterial/viral enterotoxins
Exudative Diarrhoea
1. Intestinal/colonic mucosa inflamed or ulcerated
2. Extent and location of bowel involvement determines severity
Case History and Examination
1. Onset/duration of diarrhoea
2. Timing of exposure to potential pathogens
  1. Travel, ingestion history, environment, antibiotics, age
3. Character of stool - volume, presence of mucus, blood, pus
  1. Bristol stool chart
4. Associated symptoms - abdominal pain, fever, tachycardia vomiting, dehydration
E. coli
1. ETEC (Enterotoxigenic E. coli)
  1. Watery stool
  2. Low fever
  3. In small intestine
  4. Various antigens
  5. Heat-labile toxin/stable toxin (LT/ST)
    1. LT similar to cholera toxin (Ctx)
    2. ST increases cyclic GMP and bind and activates guanylate cyclase on host cell membranes
      1. Increases water and electrolyte secretion
  6. Fimbrial adhesins
2. EPEC (Enteropathogenic E. coli)
  1. Intamin and EPEC adherence factor (EAF) and bundle-forming pilli (BFP) involved in adherence
  2. Watery, bloody stool
  3. Fever
  4. In small intestine
  5. O26, O111, and others
  6. Leading cause of childhood diarrhoea
  7. Cause changes to cell ultrastructure and induce inflammatory repsonse
  8. Invasive
3. EHEC (Enterohaemorrhagic E. coli)
  1. Shiga/Vero toxin (Stx/VT)
  2. Intamin
  3. Enterohaemolysin
  4. Watery, very bloody stool
  5. In colon
  6. O157:H7, O26, O111 and others
  7. Complications - Haemolytic uremic syndrome (HUS)
  8. Toxic cell dose is 10-100 cells
  9. Mostly food/water borne
4. EIEC (Enteroinvasive E. coli)
  1. Invasive - penetrate cells
  2. Mucoid, bloody stool
    1. Shigella-dysentry-like diarrhoea
  3. Faecal leukocytes
  4. In colon/lower small intestine
  5. Various antigens
  6. Fever
  7. Lack fimbrial adhesins
5. EAEC (Enteroaggregative E. coli)
  1. Can be protracted (last longer than expected)
  2. Attach to cells in aggregative manner
  3. Bloody stools
  4. ST toxin - EAST
  5. Haemolysin
  6. Forms biofilm
6. Alcohol gells aren't effective in the presence of faeces
Laboratory Culture
1. mFC agar at 44 'C for 24 hours (indicates presence of faecal coliforms via blue colour of lactose utilization
  1. MacConkey agar at 37 'C for 24 hours
    1. 0.85% saline
      1. IMViC tests (at 44 'C for 48 hours)
        Indole test (incubate in 1% tryptone) - Kovac's
        Methyl Red
        Voges-Proskauer
        Citrate agar - blue growth
      2. EC-MUG - fluorescence, gas
  2. ChromAgar at 37 'C for 24 hours
2. On TC-SMAC (sorbitol-MacConkey agar), sorbitol-fermenting bacteria; including E. coli form pink/red colonies
  1. On Rainbow agar O157/R&F E. coli O157:H7 agar, colonies are blue/black
3. +ve latex agglutination
Serotyping
1. E. coli can be differentiated based on antigenic differences
  1. O antigen of LPS
  2. H antigens/flaggela
  3. F antigens/fimbrae
2. Sub-catgories (pathotypes) based on pathogenicity
  1. EHEC/STEC
  2. EPEC
  3. EIEC
  4. ETEC
  5. EAEC/AEEC
  6. Further classified into virotypes based on virulence genes
    1. Fimbrial adhesins
    2. Enterotoxins
    3. Cytotoxins
    4. Capsule
    5. LPS
EcL approach to identification of pathogenic E.coli
1. Sample
  1. Enrichment (overnight)
    1. Multiplex PCR
      1. Rapid evaluation of virulence potential of pathogen (pathotype)
    2. E. coli isolates cultured
      1. Virotyping (multiplex PCR/colony hybridization)
        Serotyping
        Pulse typing (PFGE)
        Identification and virotyping of the isolate

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E. coli and Diarrhoea

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	Created by maisie_oj about 11 years ago