Jennings_LabReport18and19

Lab Report 18: Culture Media Preparation 1. Differentiate between complex and defined media. A complex medium is a medium that utilizes rich extracts of meat or plants supplying all of the amino acids, vitamins, nucleotide bases and other growth factors required by the organism. A defined medium is one in which the chemical compound is known and is specific and therefore exactly weighed out to make up the medium. 2. Name six basic nutritional requirements supplied in all culture media. Nutritional requirements for all culture media include a carbon source, an energy source, nitrogen, minerals, vitamins and growth factors, and water. 3. What growth factor is often supplied for the cultivation of fastidious bacterial pathogens? Vitamins and growth factors may often be supplied for the cultivation of fastidious bacterial pathogens. They may grow better if blood or serum components are incorporated into their media. 4. What bacterial forms are destroyed by autoclaving to avoid contamination? Autoclaving achieves sterilization by heating media to 121 degrees Celsius for at least 15 minutes at 15 psi of steam pressure. This will kill cells and endospores. 5. An autoclave is typically used for sterilization of media. a. Define sterilization. Killing or removing any contaminating bacteria that was, or may be introduced. b. Under what conditions are media typically sterilized in an autoclave? By heating media to 121 degrees Celsius for at least 15 minutes at 15 psi of steam pressure. c. What type of media components cannot be sterilized in an autoclave? Media containing vitamins cannot be sterilized in autoclave due to high temperatures. d. What is an alternative to autoclaving for sterilizing heat-sensitive materials? These items may be filter-sterilized by passing a solution through a bacteriological filter of 0.45 microns which will retain any cells or endospores, then this filter will be added to sterilized medium. 6. What compounds or chemicals might be added to a medium to make it selective? Antibiotics, dyes and some various inhibitory compounds may often be incorporates into media for it to be served as a selective medium. 7. Agar is a solidifying agent used in media preparation. a. What is its origin? Agar is a complex polysaccharide from seaweed. b. What makes it ideal for the cultivation of microbes? Agar is ideal as it melts at 100 degrees Celsius, but does not solidify until it cools to 45 degrees Celsius which allows for bacteria to be inoculated into the agar media without killing the cells. Agar is also not a nutrient for most bacteria. c. How and why does the agar concentration in semisolid media differ from conventional solid media? The semisolid concentration is at 0.4% and is done so for motility studies.