Molecular structures and biological activities of Clostridium botulinum toxins.

Clostridium botulinum is known to produce an extremely potent neurotoxin. In 1922, Bengtson isolated a nonproteolytic C. botulinum strain from Lucilia caeser larvae.1 The toxin produced by this strain was not neutralized with anti-botulinum type A or type B toxin serum. Types A and B were the only C. botulinum types known at the time. For this reason, the new strain was designated C. botulinum type C. Since then, a number of C. botulinum type C and D strains have been isolated. However, the immunological cross - reactions of toxins produced by type C and D strains have not been clearly elucided. In 1935, Mason and Robinson reported that type C strains produced three toxins, C1 and C2 and a small amount of D, and that type D strains produced a small amount of C toxin in addition to a large amount of D toxin.4 Jansen also reported that a type C2 strain produced C1, C2 and D toxins, that a type Cβ strain produced only C2 toxin, and that a type D strain produced C1 and D toxins.3 It was also reported that non- toxigenic type C and D strains, either cured of their prophages or isolated from environmental sources, produced C2 toxin.2,6 Although it had been recognized that certain strains of C. botulinum types C and D produced C2 toxin in addition to C and D toxins, little was known about the molecular structure and the biological activity of C2 toxin until the toxin was purified and characterized.