This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
Opacity around colonies of Clostridium perfringens is due to - 
Select and explain. 
A. Theta toxin, B. Lecithinase, C. Desmolase, D. Cytokinin
B: Lecithinase
Answer: B: Lecithinase 
Explanation: Opacity around colonies of Clostridium perfringens is due to lecithinase. Option 1 Theta-toxin- hemolysin & cytolytic toxin. Option 2 Nagler reaction: Shown by C. perfringens as opalescence on serum or egg yolk media due to Lecithinase C activity of alpha toxin, it splits lecithin into phosphorylcholine and diglyceride in the presence of Ca2+ and Mg2+ ions.(Refer to the image below) It is a neutralisation reaction. Option 3, 4 - Desmolase: It is not produced by Clostridium perfringens. - Cytokinins (CK) are a class of plant growth substances (phytohormones) that promote cell division, or cytokinesis, in plant roots and shoots.