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Lab report 3 - lab
Microbiology (BIO-205)
Grand Canyon University
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Identification of Unknown Bacteria Stephanie Aguilar Grand Canyon University BIO-205L March 1, 2021
Identification of Unknown Bacteria Aim : The aim of this lab is to find out the genus and species of an unknown bacteria. In this lab students will learn to perform biochemical tests, selective and differential media, and rapid membrane in order to find the identity of the unknown bacteria. Materials and methods: Materials:
- 24 hour unknown bacterial culture broth
- Glass microscope slides
- Bunsen burner
- Inoculating loop
- Permanent marker
- Gloves
- Hydrogen peroxide
- MSA plate 9 plate Procedure:
- Using a inoculating loop streak the organism onto a NA plate for colony isolation and incubate at 37C for 24 to 48 hours.
- Using a inoculating loop streak the organism onto one MAC plate for selection and differentiation analysis
- If the MAC plate shows no growth from the organism then is it Gram-positive. Students will then proceed with the various tests for Gram-positive. Gram-Positive Tests
+ OR -
a. Nutrient Agar +
-cream color -thick growth -clusters of colonies
b. MAC Plate +
-No growth -No media color change remained tan
c. Catalase Test +
-Bubbles
d. Pigmentation +
-No color
e. Mannitol Salt Agar Plate
+
-Red media -No media color change remained red
This table list the steps and results of test done to indicate whether the bacteria is positive or negative. Discussion: Bacteria are microscopic organisms that can be found everywhere. Bacteria could either be good bacteria which can help us or bad bacteria which can be harmful to us. When identifying bacteria characteristics are used like gram staining, growth, medium, and color. Bacterial identification in a lab is done in a series of steps including selective and differential
This illustrates the results of mannitol salt agar plate. In this plate there was some growth on the plate. There was no color change. The media from the plate remained a red color. The results from the plate indicated a gram- positive bacterium.
Steps Results
media. Selective media is made up of unique ingredients that stop certain microbes from developing in a mixed culture while allowing others to grow. An example of selective media is MAC plate which was used in this lab. Differential media is composed of unique ingredients in growth media that enable visual observation to differentiate specific species or groups of bacteria. An example of differential media is blood agar. Selective and differential media are both used in order to isolate or identify particular organisms. Selective media promote the growth of some species while inhibiting the growth of others while differential media are used to distinguish species or classes of organisms that are closely related. Biochemical tests are performed to identify bacterial species by differentiating them. This is done based on the differences in the biochemical activities of different bacteria. Another test used to identify unknown bacteria is rapid membrane analysis. Both tests include UTI rapid membrane and Esculin rapid membrane. In both test plates are incubated for only 1-2 hours and observe the color development. The first step to the lab was to perform a streak plate isolation on a nutrient agar for the unknown bacteria (#1). Once isolated onto a nutrient agar plate the plate had to incubate at 37C for 24 to 48 hours. Another streak plate isolation is performed onto a MacConkey Agar (MCA) plate for selection and differentiation analysis. MAC test is done in order to identify if the bacteria is gram positive or gram negative. The MAC test revealed no growth on the media indicating that it was gram positive. Once identifying the bacteria is gram positive, tests for identify what specific gram-positive bacteria it is. The next test is the catalase test to indicate if it is positive or negative for catalase. The catalase resulted with bubbles indicating that it is positive. The pigmentation of the bacterial colonies grown on the NA plate appeared as a cream color. The last step of the lab was the Mannitol Salt Agar plate. In this test if the bacteria is able to ferment mannitol it will turn the media a bright yellow if not it will stay as a red media. The unknow bacteria did not ferment mannitol so the media remained a red
Lab report 3 - lab
Course: Microbiology (BIO-205)
University: Grand Canyon University
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