Assay in mice for low levels of Clostridium botulinum toxin.

When botulinum toxin at a low level such as 0.1 to 1.0 mouse intraperitoneal LD50 was injected subcutaneously into a mouse at the inguinocrual region, abdominal ptosis with local palsy developed. If this symptom is taken as a marker, 1.0 mouse intraperitoneal LD50 can be detected within 6 h and 0.1 LD50 within 24 h. The severity of symptoms and the time-to-death in days after injection of toxin were converted into scores to quantify the toxic activity. Over a wide range of dose, between 0.075 and 38.4 mouse intraperitoneal LD50, a linear relationship was obtained between the log dose and the score. By use of this method, low levels of toxin such as 0.1 mouse intraperitoneal LD50 can be titrated accurately and easily.