HandsOn 18 - Bacterial Growth

I. Bacterial Growth Preparation

II. Streaking and Innoculating Plates

III. Growth of Bacteria Under Starvation Conditions

IV. Staining Bacterial Colonies

II. Streaking and Innoculating Plates

Cultures ordered from a supply company or stock center will probably not consist of genetically identical bacteria. The bacteria will all be of the same species, and available as a single strain. However, random mutations may still exist due to the large number of bacteria present. To obtain a source of genetically identical bacteria, streak plates are used. Streaking a plate allows the bacteria to be spread out so that a single bacterium can be isolated from all other bacteria. This technique is called streaking for individual colonies. Since bacteria are so small, you will not be able to see that isolated bacterium. However, that bacterium will reproduce itself by binary fission (typical division time is on the order of 20 minutes), resulting in bacteria which are genetically identical to the original bacterium and to each other. These bacteria are visible as a small round colony growing where there had been one isolated bacterium. This method allows you to use the individual colony repeatedly and expect similar results.

There are several acceptable streak plate methods. The method described here is called the "T'' streak and is one of the easiest.

Once you have a streak plate with individual colonies, you should inoculate, from an individual colony, nutrient agar plates containing various concentrations of nutrients.

Caution: When disposing of unwanted bacterial colony plates, you must first autoclave them. This will kill the bacteria, and make the plates safe for disposal in a regular trash bag.

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