Thioglycolate agar is an example of which type of medium?

Thioglycolate agar is an example of which type of medium?

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

Answer: (C)

Oxygen availability and how media reveal an organism’s aerotolerance is what this item tests. Thioglycolate agar is a reducing medium that lowers dissolved oxygen and creates an oxygen gradient from the top (more oxygen) to the bottom (less oxygen). The reducing agent (and often a redox indicator) lets you see where oxygen is present. This setup lets you observe where different organisms grow: obligate aerobes near the surface, obligate anaerobes at the bottom, and facultative anaerobes that can grow throughout but may be more abundant where there’s more oxygen. Because its main purpose is to support growth under reduced-oxygen conditions and to study oxygen tolerance, it’s classified as an anaerobic medium. It isn’t primarily used to enrich fastidious organisms or to selectively inhibit others, so it’s not best described as enriched or selective. It can show differential growth along the gradient, but the defining feature is its support of anaerobic (low-oxygen) growth.