Purpose: The purpose of the this experiment is to learn to transfer microorganisms to a nutrient medium to promote growth using aseptic techniques. which are a method used to prevent unwanted organisms from contaminating a medium. We will also learn about different types of culture media, including MRS broth and nutrient broth, learn about oxygen and temperature requirements for microbial growth and how to control microbial growth.
Procedure: There are four parts to this experiment. The first step is to set up an incubation site. The incubation site needs to be an area that is out of the way, can maintain a constant temperature and is free from draught. Refer to the course information tab on the class website for instructions on how to build an incubator. The microbes in this experiment have different temperature requirements: one type is best grown at room temperature while the other requires a temperature similar to that of our physical body (between 35 and 37 degrees Celsius).
The second step is to select the appropriate medium for the specified microbe. In this experiment we will use a liquid broth medium for both cultures. The first is MRS culture medium, which contains polysorbate, acetate, magnesium and manganese to promote growth for lactobacilli. The second is nutrient medium, which is the standard growth medium for most microbes. It contains heat stable digestive products of proteins called peptones and beef broth to promote bacterial growth.
Third, we will inoculate the test tubes containing the appropriate medium with L. acidophilus and S. epidemidis using aseptic techniques. Refer to pages 91-93 of the lab manual for step-by-step instructions. The MRS broth will be inoculated with L. acidophilus and the nutrient broth will be inoculated with S. epidermis.
The final step is to observe the microbial growth and record observations. Check the samples in the incubator at 24 hours. If you do