Actin-specific ADP-ribosyltransferase produced by a Clostridium difficile strain.

By screening possible ADP-ribosyltransferase activities in culture supernatants from various Clostridium species, we have found one Clostridium difficile strain (CD196) (isolated in our laboratory) that is able to produce, in addition to toxins A and B, a new ADP-ribosyltransferase that was shown to covalently modify cell actin as Clostridium botulinum C2 or Clostridium perfringens E iota toxins do. The molecular weight of the CD196 ADP-ribosyltransferase (CDT) was determined to be 43 kilodaltons, and its isoelectric point was 7.8. No cytotoxic activity on Vero cells or lethal activity upon injection in mice was associated with this enzyme. CDT was neither related to C. difficile A or B toxins nor to C. botulinum C2 toxin component I. However, Vero cells cultivated in the presence of C. difficile B toxin had a lower amount of actin able to be ADP-ribosylated by CDT or C2 toxin in vitro. Antibodies raised against CDT reacted by immunoblot analysis with a 43-kilodalton protein of C. perfringens type E culture supernatant producing the iota toxin.