lab_06_smear_simple_stain

lab_06_smear_simple_stain - Miramar College Biology 205...

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Lab Exercise 6: The Smear and Simple Staining Page 1 of 3 Miramar College Biology 205 Microbiology Lab Exercise 6: The Smear and Simple Staining Background Smears The preparation of a good smear is the backbone of all of the staining techniques you will master throughout this course. A good smear consists of three major things: 1. Heat fixing /adhering the cells to the slide so that they are not washed off during subsequent staining procedures. 2. Heat fixing gently so as not to cause distortion and artifacts to the slide. 3. Preparing a thin smear , because the thickness will determine whether or not you can visualize individual cells, their arrangement or details regarding Gram reaction or internal structure. Simple staining The use of a single stain or dye to color a bacterium is called a simple stain (Figure 1). These types of dyes, called basic or positive dyes , are positively charged, containing cationic chromophores. Because all cells are negatively charged (-70mV), there is an attraction between the positive dye and the negative cell. Some common basic dyes used in staining are methylene blue, crystal violet and basic fuchsin. However, not all dyes are positively charged. Acidic or negative dyes are negatively charged, containing anionic chromophores, and do not stain bacterial cells. They are usually used for negative staining protocols and you will get experience with this in future labs. Common acidic dyes are nigrosin, India ink and eosin. Figure 1: Simple stain of Staphylococcus aureus using the basic/positive dye Methylene Blue. Note the staphylococcal morphology and arrangement of the cells. Staining microbial cells is important because without stain, most bacterial cells are extremely difficult to see.
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lab_06_smear_simple_stain - Miramar College Biology 205...

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