<P> 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 . Once stained as part of a sample, these organisms can resist the acid and / or ethanol - based decolorization procedures common in many staining protocols, hence the name acid - fast . </P> <P> The mechanisms of acid - fastness vary by species, although the most well - known example is in the genus Mycobacterium, which includes the species responsible for tuberculosis and leprosy . The acid - fastness of Mycobacteria is due to the high mycolic acid content of their cell walls, which is responsible for the staining pattern of poor absorption followed by high retention . Some bacteria may also be partially acid - fast, such as Nocardia . </P>

What does it mean when a bacterium is described as being acid fast
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