Based on Fastidious Anaerobe Agar Base with added Egg Yolk Emulsion, this medium can be used to test Clostridium perfringens for phospholipase production. A zone of opalescence around the colonies is indicative of a positive reaction. It can also be used as an aid to identification of Clostridium perfringens if antitoxin is spread onto half of the plate prior to inoculation (Nagler Reaction).