AcidfastStain

Acid-fast staining is a differential staining technique used in microbiology to identify bacteria with a waxy cell wall, primarily mycobacteria. These bacteria contain large amounts of mycolic acids in their cell walls, which resist decolorization by acid-alcohol after being stained with a primary dye. The characteristic red or pink color of acid-fast bacteria contrasts with the blue or green color of non-acid-fast bacteria, which are decolorized and counterstained.

The most common acid-fast staining procedure is the Ziehl-Neelsen method, which uses carbolfuchsin as the primary stain, heated to aid penetration of the waxy cell wall. Acid-alcohol is then used as the decolorizing agent. Finally, a contrasting counterstain, such as methylene blue or malachite green, is applied to color the non-acid-fast cells. An alternative method, the Kinyoun method, uses a stronger concentration of carbolfuchsin and does not require heating, making it safer and more convenient for some laboratory settings.

Acid-fast staining is crucial for the diagnosis of diseases caused by acid-fast bacteria, most notably tuberculosis caused by Mycobacterium tuberculosis. It is also used to identify other clinically significant mycobacteria, such as those causing leprosy. The presence of acid-fast bacilli in a clinical sample, such as sputum or tissue biopsy, strongly suggests an infection with these organisms and guides further diagnostic and therapeutic decisions.