Why Are Agar Plates Incubated Upside Down?

Agar plates are used to culture cells and bacteria.

Agar plates are dishes of nutrient medium used to culture microorganisms and cells. They need a controlled environment and special handling.

History

Before the introduction of agar plates, researchers used foodstuffs such as bread to culture microorganisms. Later, gelatin-covered plates were used. In 1882 a researcher named Fannie Hesse suggested replacing gelatin with agar, a gelatin-like substance derived from seaweed, as a growing medium.

Features

Agar plates are small flat containers with a nutrient paste of agar. The agar is often mixed with other nutrients and also substances to inhibit the growth of unwanted microorganisms. You can use agar plates to grow cultures of cells, fungi and microorganisms such as bacteria.

Considerations

Agar plates need to be kept properly when being used to grow cell cultures. You can keep the plates in a special incubator to maintain the right temperature. However, they must be incubated upside down. This is because water evaporating from the plate may condense on the lid of the container and fall back into the culture, thus interfering with the experiment.

References

• Spiritus Temporis: Incubation of Agar Plates
• Laboratory News Features: History of the Agar Plate

Resources

• The Community College of Baltimore County: Aseptic Technique and Transfer of Microorganisms