Enterovirulent E. coli (PCR)

Stool in fecalSwab

Normally, some amount of Escherichia coli bacteria (up to 0.1% of the gut flora) live in the human intestinal tract and the bacteria are part of the gut flora.
However, some E.coli species are pathogenic due to genetic modifications, enabling them to produce toxins and/or other virulence factors, which can cause serious food poisoning or disseminated diseases like septic shock or meningitis in humans.

Infection with pathogenic E.coli often occurs via fecal–oral transmission. Common routes of transmission include: unhygienic food preparation, contamination due to manure fertilization, irrigation of crops with contaminated greywater or raw sewage, or direct consumption of sewage-contaminated water.


Pathogenic E. coli are categorised into five different pathogroups depending on their unique pathogenic trait (i.e. produced toxin or certain virulence factor):

- Enterotoxic E.coli (ETEC)
ETEC are the leading bacterial cause of diarrhea in children in the developing world, as well as the most common cause of traveler's diarrhea.
ETEC use special extensions (fimbriae) to attach to the epithelial cells in the intestine, which prevent them from being expelled by intestinal peristalsis. Also, ETEC can produce two enterotoxins: LT (heat-labile) and ST (heat-stable). The LT enterotoxin is similar to cholera toxin in strucutre and function; the ST enterotoxin causes secretion of fluid and electrolytes of cells into the instestinal lumen.

- Enteropathogenic E.coli (EPEC)
EPEC also cause diarrhea, but use an adhesin known as intimin (eae gene) to bind to host intestinal cells leading to destruction of the microvili on the intestinal wall. Further, secreted toxins disturb cell function leading to active excretion of water and ions, increased intestinal permeability, intestinal inflamamtion and finally cell death.

- Enteroaggregative E.coli (EAEC)
EAEC attach to the intestinal mucosa via aggregative adherence fimbriae and are capable of forming a biofilm (aggregation), shielding them from the rest of the gut flora. EAEC secrete various toxins leading to acute or persistent diarrhea as the bacterial excretion is slow and symptoms can persist for a long time.

- Enteroinvasive E.coli (EIEC)
EIEC invade epithelial cells in the colon, leading to inflammation and ulcer formation of the intestinal wall (but normally not beyond the submucosa) with secretion of blood, leukocytes and mucus. EIEC also produce enterotoxins which provoke a loss of electrolytes and water causing profuse diarrhea and high fever (similar to an infection with Shigella).

- Enterohemorrhagic E.coli (EHEC)
EHEC use special adhesion proteins to attach to the epithel cells of the intestinum and produces the enterotoxins shigatoxin (stx) and hemolysin. Shigatoxin has a strong cytotoxic effect while hemolysins destroy erythrocytes (haemolysis) leading to bloody diarrhoea (enterohaemorrhagic colitis).