The Microbiology And Immunology Laboratory Unknown Identification Lab Report

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The Microbiology & Immunology Laboratory Unknown Identification Project is designed to test the students’ skills and knowledge of performing biochemical tests learned during the course of the lab. Students receive a numbered tube containing a mixed culture of two unknown organisms and are required to determine the identity of each microorganism by performing a series of biochemical tests of their choice. Unknown test tube #25 was obtained and streaked onto two agar plates to obtain individually isolated colonies. The gram-staining procedure was used to determine organismal morphology, resulting in a gram-positive cocci and gram-negative bacilli. A sucrose utilization test was performed and narrowed the possibilities of the gram-negative
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Presence of acetoin results in a red medium and constitutes a positive test. The methyl red (MR) test alone is used to test for acid production and a positive test constitutes a red color. The MR-VP test can be performed on the same medium and both are important in the characterization of gram-negative non-spore-forming rods. The MR-VP test was used in determining both the unknown gram-positive and gram-negative bacteria. An inoculum of the bacteria was transferred aseptically to a sterile 5 mL tube of MR-VP medium and incubated at 37°C for two days. After 2 days, the tubes were agitated, 1 mL of the original (Tube A) was transferred into another tube, labeled Tube B. 15 drops of alpha-naphthol solution and 5 drops of 40% KOH solution were added to Tube B, mixed and results are observed. The MR procedure involves added 1-2 drops of methyl red to Tube A and observing the results. For both tests, a red colored medium is a positive test and a yellow/copper colored medium is a negative test.
The catalase test involves smearing a small amount of microorganism on a clean slide without the addition of water, adding a few drops of 3% H2O2 and observing for the appearance of bubbles of oxygen by observing the slide against a dark surface. Possible results are formation or no formation of bubbles. A positive test results if bubbles are present indicating that the catalase enzyme is breaking down the hydrogen

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