Laboratory diagnosis of botulism complicated by pyridostigmine treatment of the patient. A method for selectively removing interfering substances from clinical specimens.

In August 1974, a case of botulism occurred; home-canned potatoes and peas containing Clostridium botulinum, type A, were strongly incriminated as the vehicle of transmission. C. botulinum, type A, was isolated from a stool specimen of the patient, but the mouse neutralization test for botulinal toxin could not be completed because the stool extract contained a highly toxic, heat-stable substance that rapidly killed mice. Historical and laboratory evidence indicated that the substance was pyridostigmine bromide, a low-molecular-weight drug with which the patient had been treated after her disease was misdiagnosed as myasthenia gravis. A generally applicable method employing dialysis by which toxic SUBSTANCED of low molecular weigth could be selectively removed from specimens without diminishing the potency of botulinal toxin contained in them was developed. Dialysis rendered a pyridostigmine solution, a stool extract from the patient with botulism, and a stool extract from a person taking pyridostigmine virtually nontoxic to mice. Dialysis did not significantly alter the toxicity to mice of crude botulinal toxin; it selectively eliminated all or almost all pyridostigmine toxicity from a pyridostigmine-botulinal toxin mixture without altering the toxicity of the botulinal toxin.