BOTULISM: MYTHS & REALITIES
In the early 19th century, Justinus Kerner published a report on "sausage poisoning". Soon afterwards, microbiologist Emile van Ermengem isolated an unusual bacillus from the corpses of those who had died from "sausage poisoning" and named it Bacillus botulinus. (Botulus is Greek for sausage). The organism was subsequently renamed Clostridium botulinum, and is characterized as an extremely heat resistant, spore-forming anaerobe.
Perhaps the most dreaded and commonly cited foodborne illness, botulism is infrequently encountered and this is fortunate as it has a very high case-fatality rate. It is a severe neuroparalytic disease cause by any of the seven serotypes (A-G) of botulinum neurotoxins (BoNTs). Types A, B, and E are responsible for the majority of human cases. In adults, foodborne botulism is caused by ingestion of pre-formed toxin and with a wide range of onset times (due to amount of toxin ingested in food), symptoms include descending paralysis, starting with the head, face and neck muscles, blurred and double vision, difficulty swallowing, speaking, and eventually respiratory paralysis.
Infants suffer from a different form of the disease called "floppy baby syndrome" Their intestinal flora has not developed yet, and the C. botulinum bacteria actually colonize the gut and start to produce the toxin, causing the paralysis.
You will hear advice about never giving a baby a pacifier dipped in honey. This is partly true, but not the whole story. Infants up to 6 months are seldom given non-baby-food, and honey may be the exception. Honey originated from inside the beehive, where it becomes contaminated with bacterial spores, including from C. botulinum. They won't grow in the adult gut, but in the infant they can colonize and produce toxins. The advice should be widened to include that anything a baby places in its mouth should be cleaned and free of dust spores to it's infant system.
(Click on the question to reach the answer)
Q: I left some canned food in the back of the car for a week in summer. The temperature was very hot. Will this cause botulism> should the food be thrown out?
Q: My family have always used a boiling-water bath ( 30 minutes) for canning vegetables. Will that prevent botulism?
Q: I can tomatoes every year with a water bath at boiling point. Is this adequate?
Q: Is it true that the botulinum toxin is heat resistant, and once in the food it cannot be removed?
Q: I have heard that dented cans cause botulism; is this true?
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Q: I left some canned food in the back of the car for a week in summer. The temperature was very hot. Will this cause botulism> should the food be thrown out?
A: Storage of canned foods in a car in summer does not cause botulism or any other bacterial growth or spoilage. The inside of the can is already completely "sterile" due to the intense heat (121C or 250F) during pressure steam processing. The contents may change physically due to extended lengths of time at hot temperatures (more mushy peaches perhaps?), but there will be no health or safety issue.
Q: My family have always used a boiling-water bath ( 30 minutes) for canning vegetables. Will that prevent botulism?
A: Keep the boiling-water bath treatment just for acid foods - jams, jellies, fruits, tomato products. For all non-acid foods (fish, meats, poultry, root vegetables, green vegetables, beans, stuffed peppers, mixed vegetables in water or oil, stuffed olives) you must use a pressure-steam method, or freeze them, of preserve them in some other way (drying, salting, or pickling).
To give you some idea how resistant this organism is to heat, certain strains of C. botulinum will survive 6 hours at boiling point!
Q: I can tomatoes every year with a water bath at boiling point. Is this adequate?
A: Traditionally, it was fine. But in recent decades, growers have been marketing 'sweeter' strains of tomato in response to consumer preferences. These tomatoes usually do not have more sugar, but instead have lower acidity (higher pH). The best advice today, to keep the family safe, is to add a quarter-teaspoon of citric acid to each 500 ml (approx 1 pint), and a half tsp citric acid to a litre (approx 1 quart) of tomatoes at the canning stage.
Q: Is it true that the botulinum toxin is heat resistant, and once in the food it cannot be removed?
A: Not true. Surprisingly even though the bacterial spores are EXTREMELY heat resistant, the neurotoxins toxins are quite easy to destroy. They are broken down before you reach 80 C (176 F). This is a good fail-safe step when enjoying your family's home canning. Bring the meat, fish, veggies up to 80 C (176 F) all through briefly before you eat. Not necessary for fruits and acid foods.
Q: I have heard that dented cans cause botulism; is this true?
A: The serious food-borne illness called botulism is caused by ingestion of powerful neurotoxin that can formed in the food before it is consumed. It certainly has a connection with canned foods, in that the bacteria are strict anaerobes (will only grow in complete absence of oxygen), and the environment inside a sealed can of non-acid food will allow the bacteria to multiply and produce one of nine neurotoxins, which can be fatal.
But how does it get into the can? These bacteria can be found almost everywhere, in dust, on surfaces, or blowing in the wind. The food itself almost certainly had some spores of C. botulinum on it when it was placed in the can or jar, and we rely on proper heating after canning to kill it off. Boiling water at 100C (212 F) will not be enough. Non-acid foods need to be processed in a pressure-cooker at 15 psi (reaching 212 C or 250 F) for 20 minutes to be sure of killing off this extremely heat-resistant bacterium.
It's the inadequate heat-treatment that allows botulism to grow in canned food, not a dent.