Which test is commonly used to identify Mycobacterium tuberculosis?
RSMSSB - 2025, RSMSSB Lab Technician - 2025,
Answer: A
The stain used is Ziehl-Neelsen staining.
Mycobacterium tuberculosis has a waxy, mycolic-acid-rich cell wall that resists ordinary stains. In Ziehl-Neelsen staining, hot carbol fuchsin is driven into the wall and the bacilli then hold the red dye even after decolourising with acid alcohol, so they appear as red acid-fast bacilli on a blue background.
Gram staining stains mycobacteria poorly. Haematoxylin is a tissue stain used in histopathology, and Giemsa stain is used for blood smears and blood parasites such as malaria.
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