Which genus includes acid-fast bacteria?

Which genus includes acid-fast bacteria?

• A. Staphylococcus
• B. Mycobacterium
• C. Escherichia
• D. Candida

Answer: (B)

Acid-fast staining works because some bacteria have a waxy, lipid-rich cell wall with mycolic acids that resists decolorization by acid-alcohol, causing them to retain the primary dye. The genus known for this trait is Mycobacterium, which includes species that stain bright red/pink with acid-fast methods. This contrasts with the other organisms listed: Staphylococcus is a Gram-positive coccus without the waxy cell wall, Escherichia is a Gram-negative rod, and Candida is a fungus—none of which are acid-fast.

Acid-fast staining works because some bacteria have a waxy, lipid-rich cell wall with mycolic acids that resists decolorization by acid-alcohol, causing them to retain the primary dye. The genus known for this trait is Mycobacterium, which includes species that stain bright red/pink with acid-fast methods. This contrasts with the other organisms listed: Staphylococcus is a Gram-positive coccus without the waxy cell wall, Escherichia is a Gram-negative rod, and Candida is a fungus—none of which are acid-fast.