Just a mention of the word "botulism" is enough to strike fear into the hearts of many.
And with reason.
The illness is rare but serious—toxins attack the body's nervous system which ultimately leads to muscle paralysis, difficulty breathing, and possibly even death.
Foods typically associated with botulism include home-canned meat and vegetables, honey (in the case of infant botulism), and more recently discovered, unrefrigerated homemade salsa, potatoes baked in aluminum foil, and garlic preparations in oil.
What is Botulism?
Botulism is a rare but potentially fatal foodborne illness caused by the spore-forming bacterium Clostridium botulinum.
The organism is widespread and naturally occurs in soil, fish, raw fruits and vegetables, but becomes a real danger when it produces toxins in food before consumption.
There are two types of botulism associated with food:
Infant botulism occurs when babies under one year old consume foods that contain bacterial spores.
Because babies have not yet developed enough natural defenses in their intestines, the spores can germinate and grow into bacteria. The bacteria then produce toxins that cause infant botulism, or ‘floppy baby syndrome’.
Adult botulism occurs when food containing the preformed botulinum neurotoxin is eaten.
The neurotoxin is one of the most toxic substances known to man, with as little as 30 ng being potentially fatal.
Symptoms usually appear within 12 hours to 2 days and may include:
● double vision
● nausea and vomiting
● and ultimately paralysis of the muscles.
Treatment of botulism, which involves an anti-toxin injection, is possible if it’s caught early enough.
However, even after a full recovery from the illness, lingering symptoms can remain for years.
Will a Refrigerator Stop Botulism?
It’s often thought that refrigeration stops all bacteria from growing.
But this is not always the case, of course, as can be seen with bacteria such as Listeria monocytogenes.
But with C. botulinum, it depends on which strain is in question.
Nonproteolytic strains that grow under refrigerated conditions (at 3.3°C/38°F and above) produce spores of low heat resistance, which means they are killed off easier with heat treatments than proteolytic strains.
Proteolytic strains are unable to grow at temperatures below 10°C/50°F, but they have a high salt tolerance and produce spores with high heat resistance.
To reduce the risk of C. botulinum growing in your refrigerator, the temperature inside should be kept below 4.4°C/40°F.
For this purpose (and to ensure peace of mind!), it might be worth investing in a refrigerator thermometer! They only cost a few dollars and could potentially be life-saving.
How Do I Know if Botulinum Spores are Growing in my Fridge?
Unlike spoilage bacteria which cause visible changes to food (e.g., texture, smell, taste, or color), pathogenic bacteria (the ones that make you sick) don’t always leave traces of their presence.
The botulinum toxin cannot be detected by smell or sight. And even just a small taste of food containing the toxin can be deadly!
According to the CDC, you should always inspect home-canned food containers properly before consuming its contents.
Home-canned or store-bought foods might be contaminated with toxins if you see any of the following:
● Discolored, smelly, or moldy food (remember that not all bacteria will show these signs!)
● Containers that are leaking, bulging, damaged, or spurts liquid when opened.
If you see none of the above-mentioned signs but are still unsure, you can taste the food after it’s been boiled for 15 to 20 minutes.
Can Any Food Cause Botulism?
It’s a popular belief that as long as bacteria have no oxygen, they won’t be able to survive or grow.
But C. botulinum is quite different.
They belong to a class of bacteria called ‘obligate anaerobes’ which means they can only live in environments that lack oxygen and might actually be harmed by the presence of oxygen.
Foods with a pH higher than 4.6 (i.e., low-acid foods) and little to no oxygen provide a favorable environment for the organism to grow and release bacterial neurotoxins which ultimately causes botulism.
Canned foods, smoked fish, sausages, and even some cooked foods can develop anaerobic conditions in which the bacteria can grow.
Home-canned foods are especially at risk.
Home canners are not always aware of the dangers of botulism and might skip steps in the canning process that could have prevented it.
Other low-acid foods that have previously been associated with botulism include:
● green beans
How to Safely Clean a Fridge or Food Growing Botulinum Spores
If you suspect that you have food containing C. botulinum, you should discard it immediately.
Do not taste it first, but instead, keep it sealed and toss it in a garbage bag. Discard the containers with their lids, and do not reuse them for other foods!
The botulinum toxin can be fatal when ingested or when it enters through openings in the skin.
Reduce your risk of contact by wearing heavy-duty plastic or rubber gloves, and wearing a face mask when cleaning your refrigerator or inspecting foods.
Disinfect Your Fridge Properly
Prepare a bleach cleaning solution by mixing ¼ cup bleach with 1 ¼ cups water.
Spray the bleach solution on all contaminated work surfaces, equipment, and clothing and allow it to sit for 30 minutes.
While wearing gloves, wipe the treated surfaces with towel paper.
Place the used towel paper in a plastic bag before placing it in the trash.
Repeat the process once more, then continue to thoroughly wash the work surfaces, equipment, and clothing.
Discard the gloves in a plastic bag and place them in the trash.
Finish off by washing your hands with warm, soapy water for at least two minutes.
How to Safeguard Against Botulism
The best way to safeguard against botulism is by heat destruction of C. botulinum spores, or by preventing the growth of spores present in the food. If not properly controlled, spores can grow into bacteria which will then produce toxins.
Fortunately, there are a few ways to reduce the risk of botulism in your kitchen:
How to Reduce the Risk of Botulism:
● When canning low-acid foods, use only approved heat processes and the right equipment. Many universities have extension websites that offer recipes and tips for proper home canning and preservation. Always make sure that the sites you visit are reputable!
● Always discard canned food containers that look swollen or damaged. Place them in a separate plastic bag before throwing them in the trash.
● Do not give honey to babies less than one year old.
● Refrigerate canned foods once opened. Oils infused with garlic or herbs should also be refrigerated for no longer than seven days.
● When preparing or holding foods, keep hot foods hot (above 60°C/140°F) and cold foods cold (below 5°C/41°F) to prevent the germination of spores and the formation of toxins.
Trying to reduce the risk of botulism in your kitchen might seem like a daunting task, but fortunately, the illness is rare.
Always apply the general food safety rules when working with food: keep raw and cooked foods separate, wash your hands when preparing foods, work on clean surfaces, keep foods at the right temperatures, and store foods correctly.
Sticking to these simple rules will not only reduce your risk of botulism but will also lessen your chances of food poisoning caused by other bacteria!
Falkenstein, D. (2014). All you never wanted to know about botulism, but should. Food Poison Journal. https://www.foodpoisonjournal.com/food-poisoning-information/all-you-never-wanted-to-know-about-botulism-but-should/
Forsythe, S. J. (2010). The Microbiology of Safe Food (6th ed.). Wiley-Blackwell Pub.
Kendall, P. (n.d.). Botulism. Colorado State University. Retrieved December 29, 2022. https://extension.colostate.edu/topic-areas/nutrition-food-safety-health/botulism-9-305/
Lynt, R. K., Kautter, D. A., & Solomon, H. M. (1982). Differences and similarities among proteolytic and non-proteolytic strains of Clostridium botulinum Types A, B, E and F: a review. Journal of Food Protection, 45(5), 466–474. https://doi.org/10.4315/0362-028X-45.5.466
The University of Georgia. (2018). Identifying and handling spoiled canned food. National Center for Home Food Preservation. https://nchfp.uga.edu/how/general/identify_handle_spoiled_canned_food.html
US Department of Agriculture. (n.d.). Clostridium botulinum & botulism. Food Safety and Inspection Service. Retrieved December 29, 2022, from https://www.fsis.usda.gov/food-safety/foodborne-illness-and-disease/pathogens/clostridium-botulinum
World Health Organization. (2018). Botulism. https://www.who.int/news-room/fact-sheets/detail/botulism