Acid fastness of tubercle bacilli is
**Core Concept**
Acid fastness is a property of certain bacteria, including Mycobacterium tuberculosis, which allows them to resist decolorization by acid during staining procedures. This characteristic is due to the presence of mycolic acids in the bacterial cell wall, which are resistant to acid hydrolysis.
**Why the Correct Answer is Right**
The acid fastness of tubercle bacilli is a result of the unique composition of their cell wall, which contains mycolic acids. These long-chain fatty acids are covalently linked to the peptidoglycan layer of the cell wall, making it difficult for acid to penetrate and decolorize the stain. The acid fastness of M. tuberculosis is a key diagnostic feature that distinguishes it from other bacteria.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the specific property of acid fastness.
**Option B:** This option is incorrect because it refers to a different characteristic of the bacterial cell wall, such as the presence of a capsule or slime layer.
**Option C:** This option is incorrect because it is a property of some bacteria, such as Nocardia, but not of M. tuberculosis.
**Clinical Pearl / High-Yield Fact**
M. tuberculosis is a classic example of a bacterium that exhibits acid fastness, and this property is used as a key diagnostic feature in the identification of the organism. The acid fastness of M. tuberculosis is a result of the unique composition of its cell wall, which contains mycolic acids.
**Correct Answer:** C. The acid fastness of tubercle bacilli is due to the presence of mycolic acids in the cell wall.