Case 112

1. Prepared by Abigayle Norwood MD and reviewed by Karen Carroll.

An adult patient with no documented past medical history presented to the emergency department with sudden onset of pain, redness, and swelling of the forearm. They reported associated fever and chills. On review of systems, they denied additional symptoms including no abdominal pain, nausea, vomiting, or diarrhea. The patient had no history of trauma to the arm. They denied the use of alcohol or drugs. On physical exam, the patient had a temperature of 38.5°C and was generally well-appearing. The forearm showed intact skin overlying a well-circumscribed area of swelling and erythema with mild tenderness to palpation. There were no changes to motor or sensory function in the upper extremity. Blood cultures were collected and he was observed for a short time in the emergency department. The patient was discharged home with a course of cephalexin for cellulitis.

One day later, the aerobic blood culture bottles from each of two sets signaled positive. A Gram stain and acridine orange stain were performed and are pictured below (images courtesy of Patricia J. Simner Ph.D., M.Sc.). All of the following organisms are included in the differential diagnosis EXCEPT?