See also:
Botulism § Prevention
C. botulinum is a soil bacterium. The spores can survive in most environments and are very hard to kill. They can survive the temperature of boiling water at sea level, thus many foods are canned with a pressurized boil that achieves even higher temperatures, sufficient to kill the spores.
C. botulinum is an
obligate anaerobe that is widely distributed in nature and is assumed to be present on all food surfaces. Its optimum growth temperature is within the
mesophilic range. In spore form, it is the most heat resistant pathogen that can survive in low acid foods and grow to produce toxin. The toxin attacks the nervous system and will kill an adult at a dose of around 75 ng.
] This toxin is detoxified by holding food at 100 °C for 10 minutes.
Growth of the bacterium can be prevented by high
acidity, high ratio of dissolved
sugar, high levels of oxygen, very low levels of moisture, or storage at temperatures below 3 °C (38 °F) for type A. For example, in a low-acid, canned vegetable such as
green beans that are not heated enough to kill the spores (i.e., a pressurized environment) may provide an oxygen-free medium for the spores to grow and produce the toxin. However, pickles are sufficiently acidic to prevent growth; even if the spores are present, they pose no danger to the consumer.
Honey,
corn syrup, and other sweeteners may contain spores, but the spores cannot grow in a highly concentrated sugar solution; however, when a sweetener is diluted in the low-oxygen, low-acid digestive system of an infant, the spores can grow and produce toxin. As soon as infants begin eating solid food, the digestive juices become too acidic for the bacterium to grow.
The control of food-borne botulism caused by
C. botulinum is based almost entirely on thermal destruction (heating) of the spores or inhibiting spore germination into bacteria and allowing cells to grow and produce toxins in foods. Conditions conducive of growth are dependent on various
environmental factors. Growth of
C. botulinum is a risk in low acid foods as defined by having a pH greater than 4.6 although growth is significantly retarded for pH below 4.9. There have been some cases and specific conditions reported to sustain growth with pH below 4.6.
