This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Clostridium, Subject name: Microbiology
Double zone of hemolysis is seen in - 
Select and explain. 
A. Staphylococcus areus, B. Streptococcus pyogenes, C. Clostridium perfringens, D. Corynebacterium diphtheriae
C: Clostridium perfringens
Answer: C: Clostridium perfringens 
Explanation: Ans. is 'c' i.e., Clostridium perfringens o Two important characteristic feature of Cl. perfringens are :-Target hemolysis (double zone hemolysis) on blood agar. It is a narrow zone of complete hemolysis by theta toxin which is surrounded by a wider incomplete hemolysis by alpha-toxin.Naegler's reaction detects alpha toxin (phospholipase or lecithinase C). When Cl. perfringens is grown on a medium with the antitoxin spread on one half of the plate, colonies on the other half without the antitoxin will be surrounded by a zone of opacity. There will be no opacity around the colonies on the half of the plate with the antitoxin, due to the specific neutralisation of the alpha-toxin.