Which organism demonstrates double-zone hemolysis on blood agar?

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Multiple Choice

Which organism demonstrates double-zone hemolysis on blood agar?

Double-zone hemolysis is a distinctive pattern where two concentric zones of red blood cell destruction appear around a colony on blood agar, reflecting two different lytic activities from the organism. Clostridium perfringens is a classic example because its potent toxins, especially the alpha-toxin (lecithinase), produce a ring of complete hemolysis adjacent to the colony plus an outer zone of partial hemolysis, giving two distinct zones. This pattern helps differentiate it from others, which typically show a single, uniform zone of hemolysis (or none) on blood agar.

Double-zone hemolysis is a distinctive pattern where two concentric zones of red blood cell destruction appear around a colony on blood agar, reflecting two different lytic activities from the organism. Clostridium perfringens is a classic example because its potent toxins, especially the alpha-toxin (lecithinase), produce a ring of complete hemolysis adjacent to the colony plus an outer zone of partial hemolysis, giving two distinct zones. This pattern helps differentiate it from others, which typically show a single, uniform zone of hemolysis (or none) on blood agar.

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