Media function and colony appearance: What do we call a culture medium that allows more than one microorganism of interest to grow, yet enables them to be distinguished by their colony morphology or reactions on the plate?

Introduction / Context:
Selecting the right medium hinges on whether you want to inhibit unwanted organisms (selective), support fastidious growth (enriched), or distinguish among organisms based on biochemical traits (differential). Many diagnostic plates combine features.

Given Data / Assumptions:

• The medium in question permits multiple organisms to grow.
• It visibly differentiates them by colony color, hemolysis, or indicator reactions.
• No explicit inhibitory agent is implied in the stem.

Concept / Approach:

A differential medium contains indicators that reveal metabolic differences. Examples include MacConkey agar (lactose fermenters turn pink), blood agar (hemolysis patterns), and mannitol salt agar (phenol red indicator changes). By contrast, selective media suppress unwanted organisms (e.g., high salt, bile salts, antibiotics), and enriched media add nutrients for fastidious growth.

Step-by-Step Solution:

Verification / Alternative check:

Diagnostic algorithms rely on differential reactions (e.g., lactose fermentation) to triage isolates rapidly before confirmatory biochemical or molecular tests.

Why Other Options Are Wrong:

Selective medium: primarily inhibits rather than differentiates.

Enrichment medium: nourishes fastidious organisms; does not necessarily distinguish them visually.

None of these: incorrect because “differential medium” is standard terminology.

Common Pitfalls:

Assuming “selective and differential” are mutually exclusive; many media are both, but this stem specifically tests the “differential” concept.

Final Answer:

differential medium