Which staining method is used to visualize Mycobacterium tuberculosis under fluorescence?

• A. Auramine-rhodamine
• B. Gram stain
• C. Giemsa
• D. Ziehl-Neelsen

Answer: (A)

Visualizing Mycobacterium tuberculosis under fluorescence uses auramine-rhodamine staining with fluorescence microscopy. The thick, waxy cell wall rich in mycolic acids makes these bacteria acid-fast, and the auramine-rhodamine dyes penetrate that wall and emit bright yellow-orange fluorescence when excited by UV or blue light. This fluorescent signal stands out against a dark background and is more sensitive, allowing easier detection of scant bacilli in sputum than traditional brightfield methods. Other stains mentioned aren’t designed for this fluorescent approach: Gram stain and Giemsa aren’t used for acid-fast organisms, and Ziehl-Neelsen is the conventional acid-fast stain viewed under brightfield rather than fluorescence.