A 7-Year-Old Develops Watery Diarrhea, Which Becomes Bloody, Frightening Him $G_s$

A 7-year-old develops watery diarrhea, which becomes bloody, frightening him. He is afebrile but becoming very ill. Macroscopic examination of the feces shows no areas of pus; microscopically, there was no excess of PMNs over that expected from peripheral blood. If his disease is a result of a trip to a Wisconsin dairy farm and petting cattle, what is most likely causing the bleeding?

A) A toxin binding to $G_s$ , shutting off protein syntheses
B) Invasion of M cells with shallow ulceration, resulting from actin C
C) Polymerization, "jetting" the bacterium laterally
D) A toxin nicking the eukaryotic ribosome, shutting down protein synthesis and damaging the mucosa
E) Invasion of intestinal cells with transit to the bloodstream and reinvasion