A 62 year-old man presents to the emergency room with a 2 day history of pain, swelling, and a bad smell in his right foot. He has a history of diabetes mellitus for which he takes tablets. He denies any history of injury to his foot. On physical examination, his blood pressure is 140/82 and his temperature is 39.4. There is a deep ulcer on the plantar surface of the foot with edema and cellulitis extending to the ankle. Compression of the mid-foot produces pus in the ulcer.