A 34-year-old man who immigrated from Southeast Asia 6 months ago presents with a 3-month history of productive cough, drenching night sweats, and a 15-pound unintentional weight loss. Chest X-ray shows a cavitary lesion in the right upper lobe with surrounding infiltrate. Sputum is collected for analysis. The laboratory reports that standard Gram stain reveals no organisms, but a second stain — using carbol fuchsin dye applied with heat, followed by decolorization with acid-alcohol and counterstaining with methylene blue — reveals numerous red bacilli on a blue background.
Which of the following best explains why this organism is not visualized on Gram stain but appears as red bacilli after acid-alcohol decolorization?