What Is a Nutrient Agar Plate?

So you're ready to culture some bacteria or yeasts for science research at school, a science lab or on your own. There are a few ways you can accomplish this, but the most common way is by using nutrient agar plates. You can buy them already prepared or make your own. Nutrient agar plates make bacteria growing easy with more accurate results.

• Using nutrient agar plates is the most convenient way to cultivate bacteria and molds.

Definition

• Nutrient agar plates are petri dishes (round, shallow dishes with loose-fitting covers) containing nutrient agar used to grow bacteria and molds. Agar (also called agar agar) is a gelatinous material extracted from marine algae. Although there are several types of agar preparations to grow bacteria on, such as animal blood agar, nutrient agar is made from beef broth and yeast extracts. Since the beginning of the 20th century, this has been the standard medium used to grow microorganisms, according to the American Public Health Association.

Expert Insight

• According to Becton, Dickinson and Company (BD), an international medical technology company, the approximate nutrient agar formula per liter is 3.0g beef extract, 5.0g peptone and 15.0g agar. These provide carbohydrates, salt , vitamins and peptone needed to create the ideal environment to grow bacteria cultures in the laboratory. The amounts can be adjusted depending on what you need.

Purchasing and Preparation

• Buy pre-poured nutrient agar plates from kits sold in science supply stores or online, usually sold in packages of 10. You can also make your own nutrient agar plates by combining nutrient agar powder with distilled water, sterilizing, cooling and mixing it, then pouring 25-35 ml per petri plate for a total of about 35 plates.

Warning

• Make sure your nutrient agar plates do not get contaminated or dried out by carefully checking them for possible growth of microbial colonies.

Tip

• If you get a lot of bubbles while pouring agar plates, gently but quickly pass a Bunsen burner flame over the agar surface--this will pop the bubbles.