The diagnosis for botulism is detecting the toxin. Since it’s the toxin, not the organism, that is solely responsible for the disease, detection of the toxin is the only definitive proof. With the recalled Fonterra WPC80, no toxin was detected from clostridial isolates in the product when grown and tested.
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The standard procedure for the detection of botulinum toxin is the mouse lethality assay. The test is based on an intraperitoneal injection into laboratory mice of sample diluted in phosphate buffer. If the sample contains toxin, the mice develop typical signs of botulism, including fuzzy hair, muscle weakness, and respiratory failure that manifests as a wasp-like narrowed waist.
C. botulinum is tested by its route of intoxication, which involves absorption of botulinum toxin into the blood and then trafficking to the nerve, binding to a receptor, internalization into the nerve and cleavage of a protein substrate.
“To my knowledge, there are no foods that are routinely tested for the spores of C. botulinum,” Dr. Johnson says. “Such testing requires considerable time and there would be so many non-existent or negative results that it would not be practical.
“That takes quite a long period, so the only test that will follow all those steps of intoxication currently is the mouse bioassay, which is very expensive, uses a number of animals, but is a very sensitive assay,” Dr. Johnson relates. “There are other assays being developed, including one in my lab in which neuronal cells are used to test for the toxin, but right now mouse assay is the only definitive test.”
There’s an alternative technique called Sulphite Reducing Clostridia (SRC) testing that is used in dairy manufacturing to ensure products are low in Clostridia such as Clostridium sporogenes, which isn’t a food safety hazard but at high levels can cause food to spoil. SRC testing is general in nature and tests for a number of different Clostridia species. SRC is not intended specifically for C. botulinum, which is almost unheard of in dairy products. Moreover, of the seven serotypes of C. botulinum, only three can cause botulism.
Even in the absence of evidence that the sulfite-reducing organisms that were detected in the WPC80 were C. botulinum, Fonterra embraced a proactive approach and complimented the SRC testing with a mouse bioassay where several mice were injected with C. botulinum and one of injected mice did have a fatality.
“But antibodies were not available at the time, so that test could have detected many lethal substances in food or in the culture medium in which the isolates were grown,” says Dr. Johnson in review of the Fonterra WPC80 testing regime.
In the end it was proven that the recalled WPC80 was not contaminated with C. Botulinum and no consumers, babies included, were ever at risk of botulism poisoning as a result of consuming this product.
“The development of rapid new tests for inexpensive screening for spores could be beneficial to the food industry,” Dr. Johnson adds. “In the future, it will be beneficial to replace the complex mouse bioassay with a complete assay, such as neuronal cells, that is more sensitive than the mouse bioassay and avoids use of animals for testing.”
Life After the WPC80 Recall
To prevent a similar food safety scare from happening again, the Fonterra Operational Review identified 20 recommendations.
People – A Focus on Food Safety
1. Create a group director of food safety and quality reporting directly to the CEO.
2. Strengthen the remit and scope of Fonterra’s Food Integrity Council, chaired by the group director food safety and quality.