Unknowns Study Help

Unknowns Study Help - Important microbiological tests...

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Important microbiological tests performed in lab to identify the genus and species of unknown bacterial isolates: Gram Stain Test Morphology of Cell Test Motility Test Acid-Fast Test Endospore Test Catalase Test Aerobic, Facultative Aerobic, Anaerobic Test Citrate Utilization Test Methyl Red and Vogues Proskauer Test Urease Test Indole Test Lipase Test Amylase Test Nitrate Reduction Test Carbohydrate Fermentation Test Gelatin Liquefaction Test Gram Stain Test This test uses a differential stain called gram stain. The first step of this test is to apply crustal violet stain to the slide containing the heat fixed bacteria. Next, iodine is added to further enhance the crystal violet stain by forming a crystal violet-iodine complex. The most critical step in the test is decolorization by washing the slide in alcohol. The resulting color or lack of color determines whether the bacteria is Gram positive or gram negative. Gram positive bacteria are not decolorized by the alcohol due to the alcohol which makes their cell wall less porous and retains the crystal-violet stain. On the other hand, Gram negative bacteria are decolorized by the alcohol because their cell walls become more porous and cannot retain the crystal violet stain. A counter stain, safranin, is then used to differentiate the gram positive and gram negative cells. Gram positive bacteria stain purple while Gram negative bacteria stain red. Morphology of Cell Test This test involves taking the slide with the Gram positive or Gram negative bacteria and applying immersion oil. The oil increases the resolution of the bacteria while looking through the low power magnification lens. You then observe the shape of the bacteria, rod or cocci. The cell shape leads you to the next test of the flow chart in the Micro. Lab manual.
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Motility Test This test identifies motility in bacteria. By using the stab inoculation technique the bacteria is transferred into the motility agar tube. The agar has low concentration of nutrients in comparison to nutrient rich agar. Motile bacteria grows outwards from the stab towards the edges of the test-tube. Acid-Fast Test This test examines whether the bacteria cells can retain the primary stain after being treated with acid-alcohol. Acid- fast bacteria cells are saturated with thick waxy material called mycolic acid. This make smearing the bacteria to a glass slide difficult. More bacteria is needed to be mixed with a drop of water. The smear is treated with Carbolfuchsin as the primary stain. It is lipid soluble and penetrates the cell wall. Steam heating further enhance the stain by ‘driving’ it into the cell wall. The slide is then washed in alcohol which decolorizes non acid-fast cells. The
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This note was uploaded on 05/11/2011 for the course BIO 31 taught by Professor Silva during the Spring '11 term at Reedley.

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Unknowns Study Help - Important microbiological tests...

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