Learning objectives The student will be able to Recognize an

Learning objectives: The student will be able to: Recognize and explain what ingredients make a medium defined, complex (undefined), liquid, solid, and/or semi-solid. Convert masses of ingredients to achieve a desired volume of a medium. Explain how to adjust a medium to the required pH. Explain when (at what point in their preparation) different types of media are to be sterilized in the autoclave. In Lab: Students will: Working as a table team, prepare 150 ml of one of the following bacterial growth media: Tryptic Soy Broth, Tryptic Soy Agar, Glucose Broth. Yeast Extract Broth, Glucose Salts Medium, or LB Agar. After the media are made, each team will fill one set of 12 tubes of the medium they prepared. After lab, these tubes will be autoclaved to sterilize the media. Lab Notebook: Check the recipe for your assigned medium on the next page. Revise the recipe to make 150 ml of the medium. Show your work (calculations) for all ingredients! To gain additional practice, now revise the recipe to make 550 ml of the medium. Show a sample calculation for one of the ingredients. Look at the recipes for each medium; Is each medium complex or defined and what ingredient (s) make it so? Look at the recipes for each medium: Is each medium liquid, solid, or semi-solid and what ingredient(s) makes it so? Suppose you were making a medium that should be pH 6.6-7.0. After mixing all the ingredients, you find the pH is 8.4. What will you add to adjust the pH, and why? After lab, your medium will be put into the autoclave to sterilize it. What would happen to your media if it were not autoclaved after lab?

Solution

5. By adding dilute HCl drop by drop one can decrease the pH of the medium. While adding the medium constant stirring should be done and pH meter should be put in the medium for constant evaluation of the pH.

6. Autoclave sterilise the medium by using pressurized steam and inactivaton of bacteria, fungi, spores etc is done. If the media is not put for autoclaving the organisms will not be inactivated and will interfere with the actual purpose of the media afterwards.