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What is a Smear
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Thin layer of cells on a glass microscope slide
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Types of smearing techniques
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Broth culture and slant culture
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What is fixation
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A technique that permanently adheres bacterial cells to the slide and preserves them in a non-living state without cell distortion of cell morphology.
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Commonly used fixation
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Heat fixation
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Microbes used in Mod 4 Lab
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Serratia marcescens and Staphylococcus aureus
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Main difference between smear preparation of Broth vs. Solid (slant/plate)
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The solid smear will involve using diluted water
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How do you distinguish a good smear form a poorly prepared smear
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A good smear will be a thin, whitish layer or film. It will aslo have the microbes separated well so that the shape and grouping can be seen.
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Why is heat fixation necessary
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It will permanently adhere the bacterial cells to the slide and also preserve them in a non-living state with no distortion of cell morphology
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How is heat fixation done
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Passing the bacterial smear 2-3 times over a medium flame of a Bunsen burner then allowing it to cool before staining
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Why staining is necessary before microscopic observation of the smear
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Since all cells have a large percentage of water, the cells are very transparent when seen under a light microscope. Staining makes the contrast more visible
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Types of stains and examples
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Simple, Differential and Special
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Simple staining technique
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1 dye is used and all cells retain the stain. Can determine cell morphology and cell grouping.
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Differential staining technique
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2 different dyes. Cells differentiated by end color. Can determine cell morphology, cell grouping, and distinguish one category of bacteria from another category. (gram staining and acid-fast staining.)
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Special staining technique
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Used to highlight and identify bacterial structures. (endospore, flagella, capsule staining.)
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Shapes of bacteria
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Sherical round coccus. Spiral spirillum. Rod bacillus. Curved rod vibrio.
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