What type of media differentiates organisms based on a biochemical trait, such as lactose fermentation?

• A. Minimal media
• B. Enriched media
• C. Differential media
• D. Selective media

Answer: (C)

Differential media are designed to reveal differences in metabolism among organisms by producing observable changes when a specific biochemical trait is present. Lactose fermentation is a classic trait used for differentiation; organisms that ferment lactose produce acid, and a pH indicator or colony color change highlights those that do ferment versus those that do not. This is what makes media like MacConkey or EMB useful: lactose fermenters appear distinctly colored or darkened while non-fermenters do not show that change. Minimal media provide only the basic nutrients and don’t reveal metabolic differences; enriched media simply boosts growth, and selective media favors some organisms by inhibitors but doesn’t inherently differentiate based on a biochemical property. Hence, differential media best fits the description.