Biobiology Lab Report

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Identification of bacteria can be a difficult process due to the fact that individual bacterial cells can possess similar structural morphology to other types of bacteria. As we have demonstrated in previous lab experiments there are key biological and chemical processes that are characteristic to different types of bacteria. Using various biochemical tests we can evaluate and detect these different processes to aid in our identification of unknown bacterial samples. The implications of these test results can be applied in the medical world when determining an agent responsible for an infection and the cause of disease. Use of an optimal decision tree to sort the results of biochemical tests helps to identify an organism while using as few …show more content…
As with all other experiments where we dealt with bacteria, aseptic techniques are necessary to prevent contaminated test samples and incorrect data. Our first procedure was to streak two agar plates to observe growth factors. A sterilized inoculating loop was used to streak first a mannitol salt agar (MSA) plate. This media is selective and inhibits the growth of Gram negative bacteria. Ideally any observable growth in this media would imply that the test organism is a Gram positive bacteria. Next a sterilized inoculating loop was used to streak a MacConkey agar (MCK) plate with our unknown organism. This is a combination media, meaning it is both selective and differential. It will inhibit the growth of Gram positive bacteria while allowing Gram negative growth. It differentiates by pigment change in response to lactose fermentation. Organisms that carry out lactose fermentation will form bright pink colonies in this media. The results of these growth medium tests will be the first step in our objective to determine our unknown …show more content…
The Lysine Iron Agar (LIA) black cap tube will be used to test decarbonation lysine, if positive for decarbonation it will have a purple slant and if negative it will be a darker red color. The LIA tube will also be used to test decarboxylate lysine, which will help us distinguish bacteria that will produce hydrogen sulfide from those who cannot. If positive for decarboxylate lysine it will have a purple butt, and if negative it will have a yellow butt. The Sulfide Indole Motility (SIM) blue cap tube is a semisolid agar and it is also used to determine sulfide production, indole formation and motility in Gram negative bacteria. We will be adding a couple of drops of Kovacs reagent following the incubation of the unknown organism. The indole combines with the reagent and if positive it produces a red layer on top of the medium. If the medium has a hazy growth throughout, then is positive for motility and if it produces Hydrogen Sulfide (H2S) a black precipitate is produced. Some bacteria can produce large amounts of stable acids and others produce a smaller amount. In order to know which ones produce more or less we will do the Methyl Red Test (MR) yellow cap tube. We will be adding Methyl Red to the broth after incubation to observe fermentation and it will turn red if pH is below 4.4 (positive result) and will remain yellow if ph is above 6.0 (negative

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