Grain Staining

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Introduction

The purpose of exercise 4 was to understand the differential staining techniques: gram staining and special stain structures. Differential staining techniques are used to help identify microorganisms based on the morphology and its ability to accept the stains used. During the staining process the cells retaining the initial stain are positive, and the cells retaining the counter or secondary stain are considered to be negative. Differential stains are used to identify microorganism based on metabolism, chemical composition or the presence of another structure. The staining techniques that are used in microbiology labs are essential in identification of the organism.

We had prepared heat fixed slides before the staining processes began from prepare cultures of the following microorganisms: Staphylococcus epidermis, Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis, Mycobacterium smegmatis, and a mixed culture of: Staphylococcus epidermis and Escherichia Coli

The staining techniques used during exercise 4 were the following: Gram staining, acid fast staining, and endospore staining. The Gram staining is a commonly used stain to determine if there is peptidoglycan present on the outside of the cell wall. The bacteria that are Gram positive have a thicker wall of peptidoglycan. The thick peptidoglycan wall allows the bacteria to accept the stain. The Gram-negative cells will lose the initial stain during the decolorization process. The addition of a counter stain, Safranin, is used to view Gram-negative cells under the microscope. The acid-fast stain is used in organisms that have Mycolic acid present their cell walls. The Mycolic acid prevents the staining technique of Gram staining to work. Mycolic acid is a waxy lipid layer. The stain is placed on the slide with the addition of steam to allow the stain to penetrate the lipid layer. The initial stain is Carbolfuchin, and the counter stain is Methylene blue. The next staining...
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