The following is from The Bug Bible – http://www.safefood.net.au/AudienceHierarchy/TheBugBible/Default.htm
From a food safety view Clostridium botulinum is one of the most important of the pathogenic foodborne bacteria because of the severity of the symptoms caused by powerful neurotoxins. In the past it has been associated with inadequately canned protein foods. Today it is relatively rare and most likely associated with home preservation of foods. Although, there is increasing concern over convenience foods and foods containing fewer preservatives, minimal processing and a greater reliance on chilling for preservation. Some of these newer foods may fall within the growth range of C. botulinum.
The organism is globally distributed and is primarily a soil organism however, certain strains can be found in sediments associated with aquatic environments.
It is an anaerobe which means it requires reduced levels of oxygen for growth and it is a spore former.
Foodborne botulism is an intoxication almost always associated with ingestion of preformed botulinum neurotoxin.
Infant botulism results after ingestion of spores of C. botulinum which subsequently germinate, multiply and produce neurotoxin in the infant’s intestinal tract. Honey has been linked to infant botulism but surveys of commercial foods including honey have not identified any with a high incidence of spores.
Storage of low acid cooked foods at ambient temperatures for extended periods can create conditions suitable for the growth of this organism. Outbreaks have occurred from baked potato stored at ambient temperature for several days and spiced onions sautéed in margarine that were kept warm and used throughout the day. Garlic butter was also implicated in an outbreak in North America in 1985. The butter was made with an aqueous mixture of garlic in soybean oil. The pH of the garlic in oil was above 4.6 and the product had been stored at ambient temperature.
The growth of other organisms like moulds has been shown to reduce the acid level in some tomato products to a level where outgrowth of surviving spores of C. botulinum occurred. Home preservation of tomatoes and tomato products is common. The product should not be consumed if mould growth is evident.
Foods particularly non acidified foods should not be stored for extended periods at ambient or warm temperatures.
It is important to follow the recommendations of the food manufacturer with respect to storage temperature and shelf life.