Final answer:
Cystine-tellurite blood agar is the differential medium used for isolating Corynebacterium diphtheriae, aiding in the identification of this pathogen due to its characteristic colony color.
Step-by-step explanation:
The differential medium used for the isolation of Corynebacterium diphtheriae is a) Cystine-tellurite blood agar. Corynebacterium diphtheriae is a gram-positive bacterium responsible for causing diphtheria, a potentially severe respiratory disease.
This bacteria is known to grow slowly and requires enriched media in culture, displaying characteristics such as forming palisades. The cystine-tellurite blood agar is effective as it not only promotes the growth of C. diphtheriae but also allows for its identification due to the reduction of tellurite to tellurium, which results in the formation of black or gray colonies which are characteristic of C. diphtheriae.