Exercise 7- Acid Fast Staining

Exercise 7- Acid Fast Staining - Non Acid-fast Primary...

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Q111Exercise 7: Acid Fast Staining 3 I. Acid Fast Staining a. Differential stain – cell wall b. Characteristics of acid fast bacteria i. Contain a high content of mycolic acids in the cell wall 1. mycolic acids = lipid-like waxes ii. Mycolic acids make cells resistant to penetration by ordinary stains and dyes c. Examples of acid fast bacteria i. Mycobacterium tuberculosis , causative agent of tuberculosis ii. Mycobacterium leprae , causative agent of leprosy iii. Norcardia sp. , cause respiratory and wound (abscess and necrosis) infections d. Acid fast staining methods i. Ziehl-Neelson Method 1. uses steam to drive the primary stain into the cell; acts as a physical mordant a. steam softens the mycolic acids, allowing the stain to enter the cells b. cooling hardens the mycolic acids, preventing the stain from washing out of the cell – cooling acts as the mordant 2. Acid fast staining procedure Step Reagent Time Acid-fast
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Unformatted text preview: Non Acid-fast Primary Stain Carbol fuchsin 5 min Fuchsia Fuchsia Decolorize Acid alcohol <30 sec Fuchsia Colorless Counterstain Methylene Blue 30 sec Fuchsia Blue ii. Kinyoun Method 1. uses a wetting agent (detergent) with the primary stain to soften mycolic acids, allowing the stain to enter e. Critical issues i. Decolorization: too much or too little will give false results ii. Age of cultures: older cells (>24 hours) are crucial as younger cells have lower proportion of mycolic acids in the cell wall iii. Dense smear: decolorizer cannot penetrate and will see mixed results iv. Always use control strains when working with unknown cultures f. Procedure i. Each student will complete two acid fast stains according to the Ziehl-Neelson Method. The organisms that will be acid fast stained are Mycobacterium sp. (#16) and Staphylococcus aureus (#6)....
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