Which organism is known for double zone hemolysis on blood agar?

Which organism is known for double zone hemolysis on blood agar?

• A. Clostridium tetani
• B. Clostridium perfringens
• C. Fusobacterium nucleatum
• D. Prevotella melaninogenica

Answer: (B)

Double-zone hemolysis on blood agar is a distinctive feature of Clostridium perfringens. This organism produces a powerful phospholipase called alpha-toxin (lecithinase) that damages red cell membranes. Around colonies, the toxin diffuses to create two concentric rings: an inner zone of complete clearing (true hemolysis) and a broader outer zone of partial clearing (partial hemolysis). The result is the characteristic double-ring appearance that helps identify C. perfringens among anaerobic bacteria. Other organisms listed do not typically show this two-zone pattern; for example, the tetanus toxin producer can cause disease without producing this specific hemolysis pattern, and the other anaerobes present different, less distinctive hemolysis patterns.

Double-zone hemolysis on blood agar is a distinctive feature of Clostridium perfringens. This organism produces a powerful phospholipase called alpha-toxin (lecithinase) that damages red cell membranes. Around colonies, the toxin diffuses to create two concentric rings: an inner zone of complete clearing (true hemolysis) and a broader outer zone of partial clearing (partial hemolysis). The result is the characteristic double-ring appearance that helps identify C. perfringens among anaerobic bacteria. Other organisms listed do not typically show this two-zone pattern; for example, the tetanus toxin producer can cause disease without producing this specific hemolysis pattern, and the other anaerobes present different, less distinctive hemolysis patterns.