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3Tues_Acid fast stain

3Tues_Acid fast stain - Lab Exercise 9 Acid-fast stain...

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Lab Exercise 9: Acid-fast stain OBJECTIVES 1. Understand the chemical basis for the acid-fast stain 2. Perform a successful acid-fast stain to differentiate between acid-fast and non- acid fast organisms. INTRODUCTION Bacteria belonging to such genera as Mycobacterium and Nocardia have cell walls containing a waxy material called mycolic acid. This material significantly affects the staining properties of these bacteria and prevents them from being stained by many routine techniques used in the lab. For this reason, the acid-fast stain is an important diagnostic tool in the identification of these organisms, specifically Mycobacterium tuberculosis , the causative agent of tuberculosis, and Mycobacterium leprae , the bacterium that causes leprosy. To visualize these bacteria, it is necessary to use techniques that make the cells more permeable to stain. Today, we will be using the Ziehl-Neelsen staining method, where the primary stain, a carbolfuchsin/phenol mix, is added to cells and heated for 5 minutes.
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