Identification of a lambda toxin-negative Clostridium perfringens strain that processes and activates epsilon prototoxin intracellularly

Clostridium perfringens type B and D strains produce epsilon toxin (ETX), which is one of the most potent clostridial toxins and is involved in enteritis and enterotoxemias of domestic animals. ETX is produced initially as an inactive prototoxin that is typically then secreted and processed by intestinal proteases or possibly, for some strains, lambda toxin. During the current work a unique C. perfringens strain was identified that intracellularly processes epsilon prototoxin to an active form capable of killing MDCK cells. This activated toxin is not secreted but instead is apparently released upon lysis of bacterial cells entering stationary phase. These findings broaden understanding of the pathogenesis of type B and D infections by identifying a new mechanism of ETX activation.

► Type B and D strains with a lambda toxin gene could not process epsilon prototoxin under tested laboratory conditions.
► Strain NCTC6121 lacks the lambda toxin gene but processes epsilon prototoxin.
► The NCTC6121 processed epsilon toxin accumulates intracellularly until cell lysis.
►  NCTC6121 epsilon toxin is less cytotoxic than epsilon toxin activated by trypsin.
► Trypsin further activates NCTC6121 toxin, so the intracellular processing is partial.