Corynebacterium diphtheria produce black or grey colonies on the following agar
**Core Concept**
Corynebacterium diphtheriae is a Gram-positive, rod-shaped bacterium that causes diphtheria. The species can be identified and isolated using specific laboratory techniques, including culture media.
**Why the Correct Answer is Right**
Corynebacterium diphtheriae produces black or grey colonies due to the production of **metachromatic granules**, which are composed of **polyphosphates**. These granules give the colonies a distinct coloration on certain agar media, such as **Tellurite agar**. The bacteria reduce tellurite ions to metallic tellurium, resulting in the characteristic black or grey color.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Corynebacterium diphtheriae does not produce black or grey colonies on **Blood agar**, which is more commonly associated with the growth of beta-hemolytic bacteria.
**Option B:** This option is incorrect because Corynebacterium diphtheriae does not produce black or grey colonies on **MacConkey agar**, which is used to differentiate between lactose-fermenting and non-lactose-fermenting Gram-negative bacteria.
**Option C:** This option is incorrect because Corynebacterium diphtheriae does not produce black or grey colonies on **Eosin methylene blue agar**, which is used to isolate and differentiate Enterobacteriaceae.
**Clinical Pearl / High-Yield Fact**
Corynebacterium diphtheriae can be isolated from the throat or nose of infected individuals, and the bacteria can be identified by their characteristic metachromatic granules and black or grey colonies on Tellurite agar. This is an important diagnostic tool for the identification of diphtheria, a serious and potentially life-threatening bacterial infection.
**Correct Answer: D. Tellurite agar**