A bacillus is a rod-shaped bacterium: an acid-fast bacillus (or AFB) is a rod-shaped bacterium which, when stained with certain compounds, retains that stain despite treatment with an acidic solution. The most medically important acid-fast bacillus is Mycobacterium tuberculosis. The term acid_fast bacillus dates from 1903.
The most common staining technique used to identify AFB is the Ziehl_Neelsen stain, in which AFB are stained a bright red which stands out clearly against a blue background. Acid_fast bacilli can also be visualized by fluorescent microscopy, and by auramine-rhodamine stain.
Acid-fast bacteria include some organisms that are not bacilli; some bacteria are termed partially acid-fast.
The property of acidfastness is related to the carbon chain length of the mycolic acid found in any particular species (Lyon H 1991).
The mycolic acid (and other cell wall lipids) present a barrier to dye entry as well as elution (washing out with solvent) and this is partly overcome by adding a lipophilic agent to a concentrated aqueous solution of basic fuchsin and partly by heating.
Acid-fastness is a physical property of some bacteria referring to their resistance to decolorization by acids during staining procedures.
The high lipid content of the bacterial cell wall in organisms like Mycobacterium is probably responsible for the staining pattern of poor absorption followed by high retention.
Feeds |
Contact