Mycobacterium tuberculosis is a Gram positive bacterium Howe

Mycobacterium tuberculosis is a Gram positive bacterium. However, the Gram stain does not work with the bacteria. Explain why the Gram stain is ineffective.

Solution

Answer : Unlike all other Gram positive bacteria, Mycobacterium tuberculosis contains a hydrophobic waxy layer made up of mycolic acids which are the major components of cell walls of these bacteria. This waxy layer prevents the penetration of Gram stains. However, these bacteria are stained using another metod called Acid fast staining m/Ziehl-Neelsen Stain. This is why, these bacteria are called acid fast bacteria.