1. Presented by Bartholomew White, MD and reviewed by Patricia J. Simner, M.Sc., Ph.D.

A young adult patient presents for emergent evaluation of headaches, fever, and emesis. The patient first began experiencing headaches 10 days prior to presentation, which would wake the patient from sleep. The patient then developed fevers 5 days later. The patient's emesis started one day prior to presentation. The patient is otherwise healthy; the patient plays sports and recently lost a deciduous tooth.

The patient was observed to be irritable, lethargic, ataxic, and confused at the initial evaluation. Physical examination demonstrated a blood pressure of 97/64 mmHg, a heart rate of 104 beats per minute, a respiratory rate of 22 respirations per minute, and a temperature of 37.3 °C (99.1 °F). A computed tomography (CT) scan of the head (Figure 1.A) demonstrated a large intracerebral mass a. Follow up magnetic resonance imaging (MRI) (Figure 1.B) demonstrated an intracerebral mass that was consistent with an abscess.



The patient was taken to the operating room and the abscess was drained. Gram staining of the sample demonstrated heavy polymorphonuclear leukocytes and light gram-positive cocci.

Question: What is the most common causative organism of atraumatic bacterial brain abscesses as seen in this case?