The Biol 2130 students and employees of a public-school system developed diarrheal illness on April 2

The Biol 2130 students and employees of a public-school system developed diarrheal illness on April 2. The cafeteria served chicken that day. On April 1, part of the chicken was placed in water-filled pans and cooked in an oven for 2 hrs. at a temp of 177oC. The oven was turned off and the chicken was left overnight in the warm oven. Symptoms of the disease included nausea, vomiting, cramping and a fever. All the patients recovered within 24 hrs. Two "serotypes" of a Gram positive, oxidase negative, coagulase positive, cocci were isolated from 32 patients. 


What is the most likely source of his infection, and how would you verify this?