A 35-year-old male from rural India presents with a 3-month history of productive cough, fever, and weight loss. Sputum smear microscopy using Ziehl-Neelsen staining shows red bacilli against a blue background. The acid-fast property of the organism is conferred by the structure marked **A** in the diagram. Which of the following best explains why this structural feature also results in resistance to many first-line anti-tuberculous drugs and necessitates prolonged culture times?