Acid-fast

From Freepedia

Acid-fast bacteria are those that, when stained with certain compound, retain that stain despite treatment with an acidic solution. The most common staining technique used to identify them is the Ziehl-Neelsen stain, in which acid-fast bacteria are stained bright red, which stands out clearly against a blue background. Acid-fast bacteria can also be visualized by fluorescent microscopy, and by auramine-rhodamine stain. Bacteria may also be partially acid-fast.

Only a few types of bacteria are acid-fast, notably members of the Corynebacterineae. Most are rod-shaped, termed acid-fast bacilli (AFB), but other forms also occur. Medically the most important AFB is Mycobacterium tuberculosis. Other species of Mycobacterium and genera like Nocardia and Corynebacterium are also notable examples.