Which stain is used to stain acid-fast bacilli?

The Kinyoun stain is specifically designed for the identification of acid-fast bacilli, such as Mycobacterium tuberculosis, the causative agent of tuberculosis. This staining method is an adaptation of the Ziehl-Neelsen stain, which employs heat to facilitate the penetration of the dye into the waxy cell wall of acid-fast bacteria. In the Kinyoun method, a detergent is used instead of heat, making it a “cold” stain.

In terms of results, acid-fast bacilli will appear bright red against a green or blue background, signifying their distinctive mycolic acid-rich cell wall. This unique characteristic is crucial for diagnosing infections caused by mycobacterial species.

Other staining techniques mentioned are not suitable for this purpose. For instance, the Gram stain is primarily used to differentiate between Gram-positive and Gram-negative bacteria based on cell wall structure. The Schaeffer-Fulton stain is used for staining spores, particularly in certain bacterial species. The Giemsa stain is typically employed for blood smears and parasites but does not provide the specificity required for acid-fast organisms. Thus, the Kinyoun stain is the correct choice for staining acid-fast bacilli.