Ubiquity of Bacteria

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Microbial Diversity and Ubiquity

Microorganisms are microscopic organisms that are so small that that they can only be visualized by the aid of a compound-brightfield microscope. While we generally cannot see individual microorganisms with the naked eye, they are present in virtually every habitat known to man. Microorganisms can be prokaryotic—the bacteria or eukaryotic—the algae, protozoa or fungi. While viruses are acellular they are also studied in the scope of microbiology because they are small and because they infect cells. While most bacterial are unicellular they can also exist in colonial or multicellular forms. In this laboratory exercise you will examine the ubiquity and diversity of various microbes that are present in the environment or inhabit the human body. Most bacteria that inhabit the body are harmless or even beneficial to humans, some bacteria are opportunistic and only become pathogenic when they are present in the wrong place at the wrong time in the potential host. As microorganisms are so omnipresent, the following exercises are designed to help you learn the importance of proper asceptic technique when handling microorganisms.

During the first laboratory exercise you will be examining the examining the presence of bacteria on inanimate surfaces and on or within the human body; furthermore, you will be examining the efficacy of various cleansing agents in reducing the amounts of bacteria associated with these habitats. To this end you will first inoculate a Tryptic Soy Broth (TSB) plate with a sample from the environment. TSB is rich in nutrients and can support the growth of a number of bacteria or fungi; therefore you will be able to isolate microorganisms from your hands or other parts of the body or from the oral cavity, from your benchtop or from other inanimate objects.

With a wax pen label the bottom of a Petri plate containing TSB-agar with your name, date, lab section, and source of the inoculum. It is important to label the bottom of your plates because the lids can sometimes fall off the top of the plate and make identification of your plate difficult.

Select a place to test for the presence of microorganisms. If you are testing the oral cavity or an inanimate surface, use the pre-sterilized cotton applicator swabs provided by your instructor. Remove the swab from the test tube (be careful not to touch the cotton tip) and immediately swab the source of your inoculum. Using the plates provided inoculate the specimen onto the plate. To do this partially open the TSB plate and while continuing to hold the plate by the lid, gently rub the cotton swab along the surface of the agar. Immediately close the plate. If you are testing for the presence of microbes on the hands, vigorously rub your hands together and gently rub one or two fingertips along the surface of the agar.

Now you will test the efficacy of various soaps, chemicals and cleaning agents. If the source of your inoculum was from the oral cavity, then brush your teeth. Use a fresh plate and a clean swab to sample the microorganism present after brushing your teeth. Now rinse out your mouth with your favorite mouthwash, use the same process while remembering asceptic technique to again sample the microorganisms present in the oral cavity. If you are sampling from your hands or from the inanimate sources, you can use similar techniques. For example, you can sample the microorganisms present on your hands before washing, after washing with your favorite soap or topical cleansing solution or the antimicrobial soap that is present in the lab, after that you can test the efficacy of the hand solution (70% alcohol) that we use in the lab.

Make certain that all three plates are labeled clearly and place the plates upside down in the 37oC incubator (plates are incubated upside down to prevent condensation from dripping down onto the surface of the agar). The plates will be incubated at that...
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