All of the following statements about enriched media are true EXCEPT:

Question

Accepted Answer

A. They inhibit the growth of Gram-positive bacteria while allowing Gram-negative bacteria to preferentially grow. ## Enriched Media: Composition and Function

**Key Point:** Enriched media supplement a basal medium with nutrient-rich substances (blood, serum, egg, etc.) to support fastidious organisms. They are NON-selective — they do NOT inhibit any particular group of bacteria. Option 2 incorrectly describes enriched media as having inhibitory properties.

### Enriched Media Characteristics

| Feature | Details |
|---------|----------|
| **Purpose** | Provide additional nutrients for fastidious (nutritionally demanding) organisms |
| **Supplements** | Whole blood, defibrinated blood, serum (sheep, horse, rabbit), egg yolk, chocolate (lysed RBCs) |
| **Selectivity** | NONE — enriched media are non-selective and support growth of many organisms |
| **Differentiation** | Some enriched media can be differential (e.g., blood agar shows hemolysis patterns) |

### Common Enriched Media

- **Blood agar** — Contains 5% sheep blood; supports fastidious organisms; differential (hemolysis patterns)
- **Chocolate agar** — Lysed RBCs release nutrients (X factor = hemin, V factor = NAD); for Haemophilus, Neisseria
- **Löffler's serum medium** — Contains coagulated serum; enriches for Corynebacterium diphtheriae
- **Egg-based media** — Ogawa, Lowenstein-Jensen (for Mycobacterium tuberculosis)

**High-Yield:** Enriched media ≠ Selective media. Enriched media ADD nutrients but do NOT inhibit organisms. Selective media INHIBIT unwanted organisms.

**Mnemonic:** **ENriched = Extra Nutrients** — think of enriched media as "feeding" fastidious organisms, not "filtering" them.

**Warning:** Do NOT confuse enriched media with selective media. Enriched media are permissive; selective media are restrictive.

Answer

B. Examples include blood agar, chocolate agar, and Löffler's serum medium

Answer

C. They contain additional nutrients such as blood, serum, or egg to support growth of fastidious organisms

Answer

D. They are non-selective and allow growth of a wide range of microorganisms

All of the following statements about enriched media are true EXCEPT:

Explanation

Enriched Media: Composition and Function

Enriched Media Characteristics

Common Enriched Media

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Feature	Details
Purpose	Provide additional nutrients for fastidious (nutritionally demanding) organisms
Supplements	Whole blood, defibrinated blood, serum (sheep, horse, rabbit), egg yolk, chocolate (lysed RBCs)
Selectivity	NONE — enriched media are non-selective and support growth of many organisms
Differentiation	Some enriched media can be differential (e.g., blood agar shows hemolysis patterns)