Question
Enterotoxigenic escherichia coli
Answer
Enterotoxigenic Escherichia coli (ETEC) is one of the major diarrhoeagenic pathotypes of E. coli, and the leading bacterial cause of traveller’s diarrhoea and a major cause of infantile diarrhoea in developing countries.
Pathogenesis: ETEC colonizes the small intestinal mucosa via colonization factor antigens (CFAs, fimbrial adhesins) without invading the mucosa, then elaborates one or both of two plasmid-encoded enterotoxins:
- Heat-labile toxin (LT) — structurally and functionally similar to cholera toxin; activates adenylate cyclase, raising intracellular cAMP, driving active chloride/fluid secretion into the gut lumen.
- Heat-stable toxin (ST) — activates guanylate cyclase, raising cGMP, with a similar net secretory effect.
Both toxins produce a profuse watery, non-inflammatory (secretory) diarrhoea without mucosal invasion or destruction — clinically resembling a milder cholera-like illness, without blood, pus, or fever.
Laboratory diagnosis: stool culture on MacConkey agar identifies E. coli but cannot distinguish the pathotype; specific identification requires detection of LT/ST genes or toxins by PCR, or ELISA/bioassay for the toxins — routine biochemical/serotyping cannot reliably distinguish ETEC from commensal E. coli.
Treatment: oral rehydration therapy (ORT) is the mainstay; antibiotics (fluoroquinolones/azithromycin) may shorten illness in moderate-severe traveller’s diarrhoea. Prevention relies on safe food/water hygiene.