A 2-year-old boy is brought to the urgent care center for evaluation. He has had a fever, pain

with swallowing or neck movement, and decreased oral intake over the past few days. Today, his

breathing quickened, and his voice became muffled. His temperature is 38.8 °C, heart rate is 130

beats/min, respiratory rate is 45 breaths/min. and oxygen saturation is 96% on room air. He is ill

appearing. He has respiratory stridor and subcostal retractions. He holds his head midline and

refuse, to move his neck or open his mouth widely, so his oropharynx is not well visualized. A

lateral neck radiograph is obtained.

Of the following, the MOST likely pathogen causing this boy’s condition is