Review Question - QID 219372

A previously healthy 2-year-old male presents to your pediatric emergency department with his parents who claim he has been walking with a limp for the last week and a half. They deny any knowledge of trauma and state that he has been ambulating since he was 11 months old. On examination, he has a mild degree of warmth about his right knee and a moderate-sized effusion. Radiographs show no fracture. Lab studies demonstrate WBC of 11,500/mm3, ESR of 60 mm/hr, and CRP of 12 mg/dL. Aspiration of the knee shows 30,000 nucleated cells with 72% PMNs. Initial gram stain and culture are negative but PCR testing is positive. You inform the parents you are concerned he may have septic arthritis of the knee. Which of the following best describes the most likely causative bacteria?