Human botulism is commonly caused by groups I and II C. botulinum.Other species of clostridia have been isolated that produce BoNTs, including Clostridium argentinense, and rare strains of Clostridium baratii and Clostridium butyricum. Neurotoxin-producing clostridia are paraphyletic, and are designated solely by their ability to produce their characteristic neurotoxin.