Thioglycolate agar is an example of which type of medium?

• A. Enriched medium
• B. Selective medium
• C. Anaerobic medium
• D. Differential medium

Answer: (C)

Thioglycolate agar is designed to reduce oxygen and create an oxygen gradient in the medium. The reducing agent thioglycolate lowers the redox potential, allowing anaerobic organisms to grow. Because of the gradient, aerobes tend to grow near the surface where oxygen is available, while anaerobes grow toward the bottom where oxygen is scarce, and facultative anaerobes can grow throughout. This setup is characteristic of an anaerobic medium, since its main purpose is to support the growth of anaerobes by providing a low-oxygen environment. It isn’t primarily about enriching nutrients, inhibiting certain organisms, or differentiating them based on other traits.