1. Presented by Cherub Kim, MD and reviewed by Patricia Simner, MSc, PhD

Clinical Vignette

A previously healthy young adult presents to the emergency department with a sore throat which started two weeks ago. The patient has been taking amoxicillin prescribed by an urgent care clinic. However, despite treatment, the patient's symptoms have worsened and now include hoarseness, dysphagia, and right neck pain. On exam, the patient has a fever and is mildly tachycardic. A complete blood count shows an elevated white blood cell count of 16.7 K/cu mm (reference range, 4.5 - 13.0 K/cu mm). The patient's right neck is tender and swollen, with a prominent external jugular vein. The right tonsil is swollen. A computed tomography (CT) scan of the head (Figure 1) shows a 2.1 cm right peritonsillar abscess. Doppler ultrasonography shows thrombosis of the right external jugular vein. The abscess is drained and sent for gram stain and culture. The gram stain is shown in Figure 2.

Which is the most likely causative organism?