A 69-year-old man presents with a 1-day history of diarrhea that was initially watery; it is now bloodstained. He lives on a farm and reports that the drinking water had recently been contaminated by cow manure. A stool examination reveals polymorphonuclear leukocytes, but no trophozoites.
What is the causative organism?
A) Staphylococcus aureus
B) Clostridium perfringens
C) Escherichia coli serotype
D) Giardia lamblia
E) Salmonella typhi
