Bacterial Structure and Staining

Which feature best discriminates between acid-fast bacteria (e.g., *Mycobacterium tuberculosis*) and non-acid-fast Gram-positive bacteria (e.g., *Staphylococcus aureus*)?

A 32-year-old woman from Delhi presents with a chronic cough and constitutional symptoms. Sputum smear microscopy shows acid-fast bacilli. Which investigation is the gold standard for confirming the organism and determining drug susceptibility?

Which of the following bacterial structures is composed of peptidoglycan and is responsible for maintaining cell shape and rigidity?

In Gram staining, which of the following is the mordant that forms a complex with crystal violet and allows retention of the dye in Gram-positive bacteria?

A 32-year-old woman presents with a painless ulcer on her genitalia with indurated borders and a clean base. Dark-field microscopy of the exudate reveals motile, spiral-shaped organisms. What is the drug of choice for treatment of this infection?