Which medium is used to grow Corynebacterium diphtheriae and yields black-gray colonies?

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Multiple Choice

Which medium is used to grow Corynebacterium diphtheriae and yields black-gray colonies?

Corynebacterium diphtheriae is identified using a selective medium that includes cystine and tellurite. On this cystine tellurite blood agar, the organism reduces tellurite to elemental tellurium, producing the distinctive black-gray colonies. The cystine supports growth, helping recovery of the bacterium. Other media don’t produce those dark colonies because they lack the tellurite component and aren’t selective for C. diphtheriae: MacConkey agar targets Gram-negative bacteria, Blood agar is non-selective, and Chocolate agar favors other fastidious organisms without creating the tellurite-induced pigmentation.

Corynebacterium diphtheriae is identified using a selective medium that includes cystine and tellurite. On this cystine tellurite blood agar, the organism reduces tellurite to elemental tellurium, producing the distinctive black-gray colonies. The cystine supports growth, helping recovery of the bacterium. Other media don’t produce those dark colonies because they lack the tellurite component and aren’t selective for C. diphtheriae: MacConkey agar targets Gram-negative bacteria, Blood agar is non-selective, and Chocolate agar favors other fastidious organisms without creating the tellurite-induced pigmentation.

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