TB and U

Acid-fast bacilli (AFB) smear An examination of a specimen (e.g., sputum) that has been spread onto a glass slide, stained, washed in an acid solution, and then placed under the microscope for examination; used to detect acid-fast bacilli in a specimen. Acid-fast bacilli are not decolorized by acid-alcohol after having been stained with dyes such as basic fuchsin.

The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain, in which the acid-fast species are stained bright red and stand out clearly against a blue background.