Common Microorganisms

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Microorganisms such as bacteria, fungus, mold, and yeast are present and common in almost every environment on earth. The normally microscopic organisms can easily be seen using differing types of agar, which creates an ideal environment for the organisms to form colonies, which are groups of hundreds of organisms that can be seen with the naked eye. In order to see individual microorganisms, it is necessary to use the magnification of a high-powered microscope. These techniques of microbiology are used in the following five experiments. The first experiment used Trypticase Soy Nutrient Agar (TSA), which can grow a wide variety of organisms and contains casein and soybean meal and a minute NaCl, to study the effectiveness of alcohol as a skin antiseptic. The second experiment tested the effectiveness of different kinds of mouthwashes as antiseptics using TSA as well. Experiment number three explored the normal human flora existing on skin and in nasal cavities, and two types of agar were used, including TSA and Mannitol Salt Agar, which contains manitol sugar, phenol red, and 7.5% NaCl. Mannitol Salt Agar tests for the presence of staphylococci bacteria that can survive in the salt that inhibits the growth of most other bacteria. Some forms of staph bacteria ferment mannitol and produce a yellow color around the colonies, which can easily be seen against the red background. The fourth experiment studied the number of bacteria in a diluted sample of uncooked hamburger meat using nutrient agar and a Quebec counter to count the colonies. The final experiment involved the growth of yeast cells under aerobic and anaerobic conditions.

- Trypticase Soy Nutrient Agar
-Mannitol Salt Agar
-Sterile alcohol swab
-Listerine mouthwash
-Tubes of nutrient agar
-Diluted hamburger meat
-Quebec colony counter
-Apple juice
-Anaerobic yeast culture
Experiment 1. Effectiveness of alcohol as an antiseptic
1) All experiments must be done in a sterile environment; Lysol can be used to sterilize the area. 2)Divide a petri plate filled with Trypticase soy agar into 4 quadrants. Label them A, B, C, and D. 3)Press the pad of a dirty thumb onto quadrant A.

4)Swab the thumb with sterile water, allow to dry, and imprint it onto quadrant B. The sterile water acts as a control. 5)Press the other dirty thumb onto quadrant C.
6)Swab this thumb with the alcohol swab, allow to dry, and imprint on quadrant D. Experiment 2. Effectiveness of mouthwash as an antiseptic
1) Divide a petri plate with Trypticase soy agar into 2 quadrants. 2) Swab the inside of your mouth with a sterile cotton swab, inoculate one half of the agar. 3) Rinse your mouth with Listerine brand mouthwash. Wait 5 minutes after rinsing. 4) Swab the inside of your mouth with a clean sterile swab, inoculate the second half of the agar. Experiment 3. Normal human flora

1)Obtain two petri dishes containing one half Trypticase Soy Agar and one half Mannitol Salt Agar. 2)Moisten two sterile swabs in sterile water, remove excess water, and then use one of them to swab the inside of your nose, and the other to swab a patch of skin, like your neck. 3)Inoculate each dish of agar with either the nose or shin swab on both sections.

Note: For experiments one through three, each petri plate should be taped shut and stored upside-down for one week at room temperature to incubate the microorganisms. During the second week, the plates with microorganism colonies can be observed.

Experiment 4. Standard Plate Count of Meat
1)Liquefy two tubes of nutrient agar in a boiling water bath.

Experiment 5. Growth of Yeast
1)Obtain anaerobic yeast cultures, made from yeast cells inoculated into bottles of sterile apple juice and allowed to ferment the sugars without contact with air. 2)Degas the culture by allowing it to stand opened for one hour at room temperature. 3)Make 10ml dilutions of 10%, 20%,...
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