Question

how does heating the bacterial smear during ziehl neelson stain promote entry if carbol fuchsin into acid fast wall? why the kinyoun procedure referred to ad the cold acid fast stain procedure? explain

Answer 1

The Ziehl Neelsen (ZN) method of staining acid fast bacilli has been in vogue for more than hundred years. In the ZN method , the basic fuchsin phenol dye is used hot there by melting the unsaponifiable waxy substance on the surface of the cell wall. However, because of disadvantages like controlled heating and non-availability of spirit for lamps there have been attempts to develop a cold staining method for tubercle bacilli....carbol fuchsin stains every cell. When they are de-stained with acid-alcohol, only non-acid-fast bacteria get de-stained since they do not have a thick, waxy lipid layer like acid-fast bacteria. When counter stain is applied, non-acid-fast bacteria pick it up and become blue (methylene blue) or green (malachite green) when viewed under the microscope. Acid-fast bacteria retain carbol fuchsin so they appear red.

In the cold staining technique, Kinyoun used higher concentrations of basic fuchsin and phenol , Tan Thia Hok [devised a method by combining the staining techniques of Kinyoun and Gabbet, and found it quicker than ZN method. Vasantha Kumari reported a variation of ZN method that permitted cold staining of tubercle bacilli by avoiding the use of heat and by increasing the staining time.