PLE-4823

A 7-month-old girl presents to the ER with a gradual onset of fever, lethargy, and irritability. Her immunizations are up to date. Examination reveals a febrile infant who is crying inconsolably. A lumbar tap is performed with the following result: WBC 1500/mm3, 84% segmenters; glucose 12 mg/dL; protein 70 mg/dL. Gram stain is negative. What is the most likely etiologic agent for this infection?