Daisy head colonies are seen with: (A) Staphylococcus aureus, (B) Corynebacterium diphtheriae, (C) Staphylococcus pyogenes, (D) Anthrax
Answer is B. A round grey or black colony with a narrow translucent scalloped border, typically produced by Corynebacterium diphtheriae on tellurite blood agar. Tellurite inhibits the growth of most other bacteria, acting as a selective agent. Diphtheria bacilli reduce tellurite to metallic tellurium, which is incorporated in the colonies giving them a grey or black colour. Reference: Textbook of Microbiology; Anathanarayan and panicker&;s; 9th edition; Page no: 237