Exercise 3-8 Micro Lab: Acid Fast Stains

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1

What is the basis for the acid fast differential stain? 

The presence of mycolic acids in the cell walls of acid fast organisms

2

mycolic acid

a waxy substance that gives acid fast cells a higher affinity for the primary stain and resistance to decolorization by an acid alcohol solution

3

Two methods of acid fast staining

1. Ziehl-Neelson (ZN)

2. Kinyoun (K)

4

Zn method of staining

uses heat as part of the staining process

uses the phenolic compound carbolfuchsin as a main stain because it is lipid soluble and penetrates the waxy cell wall.  then steam heat to melt the wax and allow the stain to move into the cell. 

acid alcohol is used to decolorize non acid fast cells; acid fast cells resist this decolorization

a counterstain such as methylene blue is applied. acid fast cells are reddish purple; non acid fast cells are blue

5

K method of staining

a cold stain

uses a slightly more lipid soluble and concentrated carbolfuchsin as the primary stain.

decolorization with acid alcohol is followed by a contrasting counterstain, such as brilliant green or methylene blue

6

What helps the acid fast cells adhere to the slide? 

a drop of serum to help the "slippery" acid fast cells adhere

7

acid fast stain

a differential stain used to detect cells capable of retaining a primary stain when treated with an acid alcohol. 

8

what bacteria is acid fast stain mostly used to detect

Mycobacterium

9

why do Mycobacterium cells clump up?

because the waxy cell walls make them sticky 

10

why do Staphylococcus clump up?

they grow in grape like clusters

11

what diseases are acid fast stains used to detect? what bacteria cause this? 

tuberculosis

acid fast bacilli (AFB)