HandsOn 18 - Bacterial Growth

I. Bacterial Growth Preparation

II. Streaking and Inoculating Plates

III. Growth of Bacteria Under Starvation Conditions

IV. Staining Bacterial Colonies

I. Bacterial Growth Preparation

To minimize contamination of your experiment by the bacteria that live on and around us, please:

This experiment requires the following supplies and equipment:

Chemicals for Nutrient Agar:

Chemicals for an Alternative Nutrient Agar Luria-Bertani (LB):

Bacteria can be purchased from supply companies (e.g., Carolina Biological Supply Company or Difco Laboratories). Specific bacteria can sometimes be obtained from stock centers. B. subtilis is available from the Bacillus Genetic Stock Center at Ohio State University and E. coli is available from the stock center at Yale University. Both stock centers provide the bacteria free to educational institutions. See the "Yellow Pages'' at the end of the book for information on suppliers.

Preparing Nutrient Agar Plates

Bacteria grow on nutrient agar. The formulas in this text are given for one liter solutions; smaller volumes than a liter can be made by scaling down the quantity of each ingredient by the same ratio as the volumes. For instance, if the formula for one liter of nutrient agar calls for 10.0 grams of agar, use 2.5 grams to prepare 250 milliliters of solution. To vary the nutrient levels in this experiment, vary the Bacto Peptone levels in the solution. The formula for the nutrient agar with 1.0 g/L of Bacto Peptone is:

Bacto Peptone Medium:

For streak plates, you can use a concentration of 1.0 g/L Bacto Peptone. There are many other kinds of nutrient agar that can be used to obtain individual colonies. Since bacteria grow differently on different kinds of nutrient agar, you may find that one works better than another for you. One standard nutrient agar is Luria-Bertani (LB).

Luria-Bertani (LB) Medium:

For this procedure, you will be using an autoclave. An autoclave is designed to produce temperatures and pressures that will completely sterilize objects. It is important that you use gloves designed for use with the autoclave so that you do not injure yourself.

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