Observations on the effect of the diluent used for diluting challenge toxin in the Clostridium botulinum potency test

Clostridium botulinum vaccines were assayed for potency according to the method described in the European Pharmacopoeia. This method uses 20 white mice which are vaccinated with a dilution of vaccine in 0.9% saline. Twenty-one days later the vaccinated mice and ten unvaccinated control mice are challenged with C. botulinum toxin and observed for 7 days. In this study the challenge toxin was diluted in two separate diluents, 0.9% saline and peptone broth. More reproducible results were achieved with peptone broth as the diluent.