Oncogenic viruses — MCQs

A 19-year-old college student presents with a 10-day history of low-grade fever, malaise, and a non-productive cough that has worsened despite a 5-day course of amoxicillin prescribed by his primary care physician. He lives in a dormitory. Chest radiograph shows diffuse interstitial infiltrates disproportionate to his relatively mild clinical appearance. A cold agglutinin titer is elevated. Sputum Gram stain shows many polymorphonuclear cells but no organisms. Cultures on standard blood agar show no growth after 48 hours. Which of the following features of the causative organism most directly explains the failure of amoxicillin therapy and the absence of organisms on Gram stain?