PLE-3303

A psychotic, indigent man with a history of multi-substance abuse has been involuntarily hospitalized for 1 week because of persistent diarrhea. A stool sample was sent for ova and parasites, revealing numerous granular, spherical, thin-walled cysts measuring 10-20 um in diameter. Trichrome stains show up to four nuclei in most of the cysts. These findings are consistent with an infection by which of the following organisms?