An 18-month-old boy is brought to the emergency department with a 24-hour history of fever, irritability, and neck stiffness. He has not received any routine childhood immunizations. Lumbar puncture yields cloudy cerebrospinal fluid with an increased neutrophil count, low glucose, and high protein. Gram stain shows small, pleomorphic, gram-negative coccobacilli. Culture and subsequent typing identify Haemophilus influenzae type b. Which bacterial component most directly contributes to this organism’s ability to resist phagocytosis by preventing opsonization?