Differential Stains: Gram Stain and Acid Fast

The use of two or more dyes to identify various bacterias.

Gram stain  This technique separates bacteria into Gram-positive (retains crystal-violet) and Gram-negative (retain Safranin dye) bacteria.

1) Crystal violet stain is used first —> fixed with iodine

2) Alcohol wash

3) Safranin dye (aka the counterstain) is used —> fixed

4) Wash and observe!

Acid Fast:  This technique differentiates Mycobacterium from other bacteria. Mycobacterium holds onto the carbolfuchsin stain (bright red), other bacteria take on the methylene blue stain (blue).

(Image 1:http://www.studyblue.com/notes/note/n/laboratory-diagnosis/deck/2617376)

(Image 2: http://www.johnes.org/goats/_Acid-fast_ileum.html)

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  • 10 August 2012
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