Staining Microorganisms

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Staining Microorganisms

Microorganisms are often first observed by coloring the specimen with a dye to emphasize the structures for examination. In order to dye, (or stain ) the specimen, it is fixed, (attached to the microscope slide). ( Tortara, Funke, Case, 2013). To carry through this staining and fixing, the microorganisms are killed and attached to the slide. There are several staining techniques to accomplish this preparation. There are simple stains, differential stains, and special stains. The stain is cationic (basic) or anionic (acidic).
Examples of cationic dyes are crystal violet, safranin , methylene blue and basic fuchsin. Examples of anionic dye are, acid fuschin, congo red and nigrosin. Simple stains are, as they are called, “simple”; they are an alcohol solution of a basic dye, and they will highlight the microorganism so the observer can examine the structures , arrangements of cells, and shape of the specimen. If needed, an additive mordant) can be added to the sample to thicken it, making it easier to see. Simple stains are the least expensive method of staining, and can be used with all microorganisms. These are effective because they stain a pure culture and do not have to be washed and re stained. Differential stains are the most widely used staining technique for examining bacteria, as the stains react differently with different cell typed. This method of staining uses the Gram stain and the acid-fast stain. Gram staining is the most useful, as it will classify bacteria into either a gram positive or gram negative group. This is carried out by applying a heat-fixed smear with a primary stain, (usually a purple dye). The dye is washed off and then covered with iodine, then a decolorizing agent (alcohol or acetone solution). Once the alcohol is rinsed off the slide is stained again with a basic red dye and examined…...

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