Sorbitol-MacConkey agar

Definition

Sorbitol-MacConkey agar is a selective and differential culture medium used to isolate and identify Escherichia coli O157:H7. It differentiates bacteria based on their ability to ferment sorbitol.

5 Must Know Facts For Your Next Test

1. Sorbitol-MacConkey agar contains sorbitol instead of lactose found in standard MacConkey agar.
2. E. coli O157:H7 cannot ferment sorbitol, producing colorless colonies on this medium.
3. Non-pathogenic E. coli strains can ferment sorbitol, resulting in pink colonies due to acid production.
4. The medium also contains bile salts and crystal violet to inhibit the growth of Gram-positive bacteria.
5. Neutral red dye is used as a pH indicator in Sorbitol-MacConkey agar.

Review Questions

• What is the primary purpose of using Sorbitol-MacConkey agar?
• How does Sorbitol-MacConkey agar differentiate between pathogenic and non-pathogenic E. coli strains?
• What components in Sorbitol-MacConkey agar inhibit Gram-positive bacterial growth?

Related terms

MacConkey Agar: A selective and differential culture medium that uses lactose instead of sorbitol to differentiate enteric bacteria.

Escherichia coli O157:H7: A pathogenic strain of E. coli that cannot ferment sorbitol, making it distinguishable on Sorbitol-MacConkey agar.

Differential Media: Culture media designed to differentiate microorganisms based on their metabolic traits.