Denoting bacteria that are not decolorized by acid-alcohol after having been stained with dyes such as basic fuchsin; e.g., the mycobacteria and nocardiae.
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acid-fast 'as-əd-.fast adj not easily decolorized by acids (as when stained) used esp. of bacteria and tissues
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adj.
1. describing bacteria that have been stained and continue to hold the stain after treatment with an acidic solution. For example, tuberculosis bacteria are acid-fast when stained with a carbol fuchsin preparation.
2. describing a stain that is not removed from a specimen by washing with an acidic solution.
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(asґid-fast) not readily decolorized by acid after staining, a characteristic of certain bacteria, particularly Mycobacterium tuberculosis, Mycobacterium leprae, and some species of Nocardia. See under stain.Medical dictionary. 2011.