Ans. is 'a' i.e. Enteroinvasive E. coli Out of the given options only Enteroinvasive strain of E.coli causes dysentery i.e. (blood in the stool). All the other strains given in the option do not cause invasion of the mucosa and cause only diarrhoea (not dysentery)Various strains of E.coli and the important questions asked about them.Enteropathogenic E.coliIt causes diarrhoea in infants and children* usually occuring as institutional outbreaks.It does not produce enterotoxin, nor are they invasive. They adhere to the mucosa of the small intestineEnterotoxigenic E.coliIt causes traveller's diarrhoea*It produces enterotoxin. The unique feature is that a strain of ETEC can produce both Heat labile toxin* and Heat stable toxinEnteroinvasive E.coliThey themselves resemble shigella and their infection resembles shigellosis (Remember that Shiga like toxin is elaborate by enterohemorrhagic E.coli*)They produce mild diarrhoea to frank dysentery and occur in adults as well as children.They have been termed enteroinvasive because they have the capacity to invade intestinal epithelial cells in vivo and penetrate Hela cells* in tissue culture.For laboratory diagnosis of EIEC, the Sereny test* used to be employed.These strains are non motile*, do not ferment lactose* or ferment it late with acid without producing any gas.Enterohemorrhagic E. coli or Vero toxigenic E.coliE.coli produce verocytotoxin* or Shiga like toxin*They can cause mild diarrhoea to fatal hemorrhagic colitisThey cause hemolytic uremic syndrome* particularly in children.The primary target for verocytotoxin appeal's to be vascular endothelial cells.The typical enterohemorrhagic coli is serotype 0157:H7 which does not ferment sorbitol unlike majority of E. coli (but Harrison writes that few species of this serotype can ferment sorbitol)Laboratory diagnosis of EHEC is established by demonstrating bacilli or verocytotoxin in faeces.