Isolated Colonies Lab Report

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Isolated Colonies and Soil Samples A. Purification of Serratia marcescens and Staphylococcus epidermis The objective was to grow isolated colonies on a nutrient agar medium (NA). Many microorganisms found in soil are able to grow on this medium. Since there are many organisms that are found in the soil, only a few of this organisms are adapted to live in this specific medium obtained. The NA plate is the first way to isolate microorganisms because the organisms that will be left on the plate will be those who can live on the complex medium. The process of isolating a colony is done by “streaking out” isolated colonies found in a sample. Streaking out uses a sterile loop to dilute the sample and distribute single cells on a section of the …show more content…
This was done by using a sterile look to obtain cells and distributing the cells on a microscope slide. To visualize the cells, the 40X objective lens was used and the microscope needed to be focused on the specimen. The results of S. marcescens and S. epidermis under phase contrast can be seen in figure 1.2. From these results I could see that S. marcescens are rods and motile, and S. epidermis are coccoid and non-motile. C. Collection of Samples for Isolation of Soil Bacteria The objective was to obtain samples from two different areas around the university to observe different microorganisms in the soil. The two locations that were chosen was near Littlefield dormitory (Sample A) and near the Biomedical Engineering building (Sample B). The procedure used to obtain these samples required using a moistened swab and sterile water. The moistened swab was inserted into the soil, below the surface, and then it was inserted and mixed into the sterile water. These two samples were then brought back into lab so that it could be streaked on two NA plates and two ACT plates. These “streaked out” samples were allowed to grow at room temperature for two days. Each member of the group was allowed to pick a specific area of one of the NA plates in order to isolate those colonies on to a new NA plate for further observation. Once the first isolation was made, the next isolation of the …show more content…
The difference between these groups can be seen in the cell wall of Firmicutes and Proteobacteria. Firmicutes tend to have a thicker cell wall, than Proteobacteria, that contain multiple layers of peptidoglycan. Unlike firmicutes, Proteobacteria contains a complex outer membrane. Proteobacteria is also called “Gram-negative” and Firmicutes are called “Gram-positive”. Under bright field microscopy and with 1000X, Gram-positive appears purple and Gram-negative is pink. My results can be seen in Figure 2.3. From this figure we can see the unknown compared with S. epidermis (Gram-positive) and E.coli (Gram-negative). In my unknown picture, there tends to be a mixture of both Gram-positive and Gram-negative. The reason these were my results could be caused because of over treatment with ethanol, heat-fixed too long, or having dense clumps of cells. According to my group, the obtained a Gram-positive stain. Since most of the cells were pink, I could guess that my sample was

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