ESCHERICHIA COLI

ESCHERICHIA COLI

1. Pathogenesis:

   • 2. Urinary tract infections: E. coli is the most common cause of urinary tract infections (90%). They possess pili that bind to urinary tract receptors.
   • 1. Intestinal (Diarrheal) diseases: Five pathogenic groups of E. coli are recognized as causing diarrheal diseases through different mechanisms
     • A) Enterotoxigenic E. coli (ETEC):
       • It causes Traveler's diarrhea and infantile diarrhea. This is an acute watery diarrhea (cholera like) usually lead to dehydration especially in infants and young children.
       • They liberate 2 types of enterotoxins:
         • a) Heat labile toxin (LT) stimulates adenylate cyclase resulting in increased cAMP which causes excretion of the chloride ion, inhibition of sodium ion absorption and significant fluid and electrolyte loss into the lumen of the gut that leads to watery diarrhea.
         • b) Heat stable toxin (ST) which is non antigenic.
     • B) Enteropathogenic E. coli (EPEC):
       • It causes outbreaks of neonatal and infant diarrhea in nurseries
         • The organism adheres to intestinal mucosa resulting in loss of microvilli, thus they prevent absorption and secretion and this leads to watery non-bloody diarrhea.
     • C) Enteroinvasive E. coli (EIEC):
       • It causes dysentery. It is not toxin producer. Stool contain blood, pus and mucous.
         • The organism invades mucosa of the ileum and colon
     • D) Enterohaemorrhagic E. coli (EHEC):
       • It causes haemorrhagic colitis, which is a severe form of bloody diarrhea
         • It follows ingestion of undercooked hamburger at fast-food restaurants
           • Some patient may end up with a haemolytic uraemic syndrome (haemolytic anaemia, thrombocytopenia and acute renal failure).
             • The organism produces a toxin called "verotoxins. It is also called shiga toxin (It destructs microvilli leading to decrease absorption).
     • E) Enteroaggregative E. coli (EaggEC):
       • It causes persistent diarrhea especially in HIV patients
         • It produces ST-like toxin and a haemolysin
           • It exhibits aggregative adherence to the mucosa in patches. They are not invasive
   • 3. Neonatal meningitis: E. coli causes about 40% of neonatal meningitis (other organisms are Group B streptococci and listeria monocytogenes).
   • 4. It is an important cause of hospital acquired infections including Urinary tract infections, wound sepsis, appendicitis, peritonitis, cholecystitis, otitis media.........etc.
   • 5. In immunocompromised host, E. coli causes bacteraemia and endotoxic shock.

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