Which clostridia produce a double zone of hemolysis around their colonies on blood agar?

Clostridium perfringens is known for its ability to produce a double zone of hemolysis on blood agar. This characteristic is linked to the bacterium's production of two types of hemolysins: alpha and theta toxins. The alpha-toxin is a lecithinase that breaks down phospholipids in cell membranes, leading to the lysis of red blood cells and resulting in a clear zone around the colonies. The outer zone of hemolysis is generally attributed to the beta-toxin, which causes incomplete lysis of red blood cells, creating a greenish discoloration.

In clinical settings, recognizing the double zone of hemolysis can be crucial, as it serves as a key identifying feature for Clostridium perfringens, which is associated with gas gangrene and food poisoning. Understanding this hemolytic pattern helps in the differentiation of Clostridium perfringens from other Clostridia species, which do not exhibit the same hemolytic behavior on blood agar.