If e.coli were to secrete a toxin that causes diarrhea in humans- what would be an advantage in this?

Answer 1

it doesnt, the bodies response is to give you diarrhea to flushout the bacterial infection. the advantage is it disposes of a lot of the bacteria in the GI tract

Answer 2

Not sure what you are asking here exactly. There are multiple strains of e.coli including ones that normal live in human intestines. Some e. coli only cause mild diarrhea, while others can cause serious life-threatening illness.