Mouse Bioassay Helps Contain Botulism Outbreak

Researchers from the Statens Serum Institut (State Serum Institute), Danmarks Tekniske Universitet (DTU, Technical University of Denmark) and Fødevarestyrelsen (Danish Veterinary and Food Administration) recently identified the source of a botulism outbreak that affected nine people in June 2018. The affected people became ill after a dinner party in Sønderborg, Denmark.

Botulism is a type of food poisoning caused by a common soil bacteria, Clostridium botulinum, which produces a neurotoxin.

Researchers Respond to Botulism Outbreak

The Statens Serum Institut scientists performed specialized diagnostics on an emergency basis in order to assist medical providers. They cultured Clostridium botulinum from patient samples and showed that it produced botulinum toxin type A. They also used the mouse lethality assay to confirm presence of botulinum neurotoxin in the patient samples. This assay is a standard procedure to detect botulism toxin and is very sensitive.

Mouse Bioassay Identifies Botulism Toxin

In the mouse botulism bioassay, patient samples are injected intraperitoneally. The presence of botulinum toxin results in rapid development of disease symptoms, such as muscle weakness and respiratory failure, typically within one-to-five days. This assay can also be used to identify which of the seven botulism toxin types are present.

Mice are treated with one of the seven antitoxins, then challenged with a patient sample which has been proven toxic in mice. By observing which mice are protected from sickness by a particular antitoxin, the assay permits identification of the toxin type.

In the case of the Danish outbreak, the mouse assay confirmed the presence of botulism toxin the blood of the affected people, with results coming as quickly as four hours after sample injection.

Identifying the Source

Follow-up investigations by DTU scientists involved testing residues of foods from the dinner party in the mouse assay. They identified a homemade lumpfish roe jelly as the source of the outbreak, while ruling out contamination of the commercial roe itself.

Practitioners of home canning know that botulism is the main risk with this food preservation method, but freshly-prepared food can also be contaminated with botulism if not handled per appropriate food safety practices. The jelly was not stored at a proper cold temperature, permitting growth of Clostridium botulinum and production of botulism toxin.

Keeping Homemade Food Safe

News of serious illness from homemade food can be frightening. For freshly-made items, proper food handling and storage is critical. According to the U.S. Food and Drug Administration, people should "never allow meat, poultry, seafood, eggs, or produce or other foods that require refrigeration to sit at room temperature for more than two hours — one hour if the air temperature is above 90° F. This also applies to items such as leftovers, 'doggie bags', and take-out foods." Check that your refrigerator and freezer are maintaining proper temperature.

Food Preservation at Home

It is possible to safely preserve food at home. In the United States, the most common form of canning is boiling waterbath canning. The boiling waterbath process does several important things:

However, waterbath canning does not kill Clostridium botulinum spores. Waterbath canning is thus only appropriate for use with foods with high acid content (pH at or below 4.6), as the spores are not able to grow under high acid conditions. The combination of food with the proper acid level and the right processing time produces a completely safe product.

Food preservation experts test recipes extensively to ensure safety, and home canners are advised to only use proven recipes when canning at home. Low-acid foods may be safely canned using a pressure canner, which allows processing temperatures of >240° F. Again, rely on proven recipes for guidance in pressure canning.

Food Safety Resources

Foodsafety.gov has a wealth of information on preventing food poisoning, including helpful charts on how long foods can be stored and recommended temperatures for cooking meat.

Safe Home Canning Recipes

The National Center for Home Food Preservation provides research-based recommendations and recipes. Cooperative extensions in many U.S. states also provide tested recipes and education on safe home canning.

Summer is the peak time for canning perfectly ripe local produce. A little education will allow you to safely preserve and enjoy those delicious local fruits and vegetables long into winter.