A non-answer.
E. coli is an organism found only in the intestines of mammals. And the strains that make people sick are pretty much limited to herbivores such as cattle and deer.
So how did the bacteria get into the flour? It certainly wasn't living in the wheat.
Vermin at the mill?Animal waste in the harvesting or storage stages?
I believe E Coli is also found in human excrement. When it has been linked to vegetables (as it has over the past few years), it was discovered a couple of times that the cause was due to the farmhands urinating and defecating right in the fields they were harvesting.
I’m not saying that’s how it got in the flour. But it could have gotten there if a patch of the wheat field was an area frequented by wildlife for urinating/defecating. It gets on the wheat. They harvest and process it. It is not irradiated or cooked, and the E Coli is alive in the flour.