Microbiology Lab Reports

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Sara Parks Unknown Report

Introduction One of the many reasons to study microbiology is to gain a better understanding of microorganisms and the huge part they play in the world. It is imperative to know the differences between microorganisms. This knowledge is useful in many cases; for instance, a patient with an unidentified infection could be administered effective treatment if one possessed the knowledge to correctly define the microorganism. Furthermore, the purpose of this unknown lab activity is to identify both a pure culture of an upper respiratory tract microorganism and two unknown species from a mixed culture of enteric bacteria. To correctly identify these organisms, students applied their acquired knowledge to perform tests
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This was streaked for isolation on a MacConkey agar plate, and then streaked once more on a separate MacConkey agar plate. Two plates were used in an effort to ensure that isolated colonies were produced. The aseptic technique was also used, and the loop was sterilized in the bactoincinerator after each streak for the same reason. The two MacConkey agar plates were placed in the incubator (35oC) and then retrieved 24 hours later. Upon retrieval, the two plates were gathered and isolated growth was seen on both plates. However, there was only a little isolated growth, so two more MacConkey agar plates were obtained. Hoping to see even more isolated colonies, we used the aseptic technique and the colonies on the existing agar plates to streak these two new plates. After another 24-hour period of incubation, much successful isolated growth was observed. This second streaking and incubation was important for separating the two unknowns into Lac+ and Lac- organisms. The MacConkey agar is selective for Gram-negative bacteria, and differential between lactose fermenters (Lac+). The tests used for identifying these two bacterial species included: MacConkey agar plating, utilization of triple sugar iron, or TSI (and H2S), citrate, and urease testing. The TSI test was done to test for the fermentation of glucose, lactose, and sucrose, and signs of a black precipitate, H2S. The citrate test enabled us to see which organisms …show more content…
Due to this distinction, the URT unknown was narrowed to: Staphylococcus epidermidis, Enterococcus faecalis, and Moraxella catarrhalis. After a Gram stain and observation of purple spheres under the microscope, the organism was learned to be Gram positive, thus eliminating M. catarrhalis. An oxidase test confirmed that both S. epidermidis and E. faecalis were oxidase negative since the organisms were clear and did not oxidize. To distinguish the two, a final confirmatory bile esculin test was performed. After incubation, the unknown tested positive for bile esculin, resulting in a black/brown color of the medium in the tube. This meant that the pure unknown bacterium tube #332 was identified and confirmed as Enterococcus faecalis. According to the lab manual table, E. faecalis is Gram positive, has no hemolysis, oxidase negative, and bile esculin positive, all of which did not have any conflict with my

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