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
A 3 yr old boy fell down and injured his leg while he was playing on ground. After a few days, there are crepitations felt from injured area, what could be the probable causative organism? 
Select and explain. 
A. Corynebacterium Diphtheriae, B. Pseudomonas Aeruginosa, C. Clostridium Tetani, D. Clostridium Welchii
D: Clostridium Welchii
Answer: D: Clostridium Welchii 
Explanation: Ans. (d) Clostridium WelchiiRef: Microbiology by Ananthanarayan and Paniker 8th ed. /643, 655, 249-54* Clostridium Welchii is also known as Clostridium perfringens.* It is the most common bacterial agent which causes gas gangrene.* Gas gangrene results in tissue necrosis, putrefaction of tissues, and gas production.* It is caused primarily by Clostridium perfringens alpha toxin, usually after a injury or trauma.* These gases form bubbles in muscle and produce characteristic smell of decomposing tissue.* The local spread of gases under tissue produces Crepitations when pressed on it.* Crepitations: sound of snow crushing* After rapid and destructive local spread (which can take hours), systemic spread of bacteria and bacterial toxins may result in death.