Carbol-fuchsin methods are specific for which group of organisms?

• A. Mycobacteria
• B. Staphylococcus aureus
• C. Candida albicans
• D. Escherichia coli

Answer: (A)

Carbol-fuchsin methods target organisms with a waxy, lipid-rich cell wall due to mycolic acids. This outer barrier allows the stain to penetrate and bind when heat is applied, and those cells retain the red color even after decolorization with acid-alcohol. That retention is what makes them identifiable as acid-fast. Non–acid-fast organisms lack this thick mycolic-acid layer, so they are decolorized and take up the counterstain, appearing a different color. Therefore, acid-fast staining is most specific for mycobacteria, such as Mycobacterium species, which explains why the correct group is the mycobacteria.