Based on the Kinyoun modified staining technique, the acid-fast stain is a very useful tool for differentiating acid-fast bacteria (AFB), such as Mycobacterium spp., from those that do not resist the acidified decolorization step. The mechanism for acid-fastness is not clearly understood, however it is suspected that it is determined by selective permeability of the cytoplasmic membrane. The brilliance of red coloration is due to retention of the carbol fuchsin dye within the cell membrane. Should the cell be mechanically disrupted, its acid-fast property is lost.
After staining, decolorizing, and counterstaining, any acid-fast bacteria present are brilliant pink to red in color, and other bacteria present are seen as blue (methylene blue counterstain) or green (brilliant green counterstain). No heating or time dependent decolorization steps are required.
INTERPRETATION OF RESULTS
The appearance of bright red stained bodies that are slender, slightly curved, long or short rods, and sometimes granular or beaded are typically acid-fast bacteria (AFB). Some atypical forms appear thick or diptheriod, sometimes coccoid, or are very long. Other non-acid-fast organisms will stain blue (or green when using brilliant green counterstain), as will background material.
Cat. no. HDAF900 With Methylene Blue Counterstain
Cat. no. HD483KB With Brilliant Green Counterstain