Acid-fastness is a physical property of certain bacterial and eukaryotic cells, as well as some sub-cellular structures, specifically their resistance to decolorization by acids during laboratory staining procedures.

What is meant by acid fastness?

Acid fastness is a physical property that gives a bacterium the ability to resist decolorization by acids during staining procedures. This means that once the bacterium is stained, it cannot be decolorized using acids routinely used in the process.

Why is TB called acid-fast?

Mycobacteria are called acid-fast bacilli because they are a group of rod-shaped bacteria (bacilli) that can be seen under the microscope following a staining procedure where the bacteria retain the color of the stain after an acid wash (acid-fast).