Microscopy of stained (Ziehl-Neelsen staining) smears taken from the sputum of a patient with chronic pulmonary disease revealed red bacilli. What property of tuberculous bacillus was shown up?

Answer options

1. Alkali resistance
2. Acid resistance
3. Sporification
4. Capsule formation
5. Alcohol resistance

Explanation

The Ziehl-Neelsen stain (acid-fast stain) is a special bacteriological stain used to identify acid-fast organisms, mainly Mycobacteria. Mycobacterium tuberculosis is the most important of this group because it is responsible for tuberculosis (TB). Acid-fast organisms like Mycobacterium contain large amounts of lipid substances within their cell walls called mycolic acids. These acids resist staining by ordinary methods such as a Gram stain. When counter-stain is applied, non-acid-fast bacteria pick it up and become blue (methylene blue) or green (malachite green) when viewed under the microscope. Acid-fast bacteria retain carbon fuchsin so they appear red.