Opinion of the Scientific Panel on biological hazards (BIOHAZ) related to Clostridium spp in foodstuffs

No abstract available

Anaerobic spore-forming bacteria spoil a wide range of foods including dairy products, meat and poultry products, fresh and canned fruits and vegetables, typically producing gas and/or putrid odours. A few of those species can cause illness.

The species of the genus Clostridium most commonly involved in food-borne illness are Clostridium perfringens and C. botulinum. Intoxication due to C. perfringens is usually brief, self-limiting, and is rarely fatal. However, the neurotoxins of C. botulinum are among the most toxic naturally-occurring substances and cause severe food-borne illness, sometimes fatal, with symptoms continuing for several months.

Clostridia occur commonly in soil, dust, the aquatic environment and in the intestines of animals. Consequently, C. perfringens and C. botulinum can be present in a wide range of foods. Good Agricultural Practices and Good Hygienic Practices contribute to reducing numbers of clostridia by minimising contamination with soil and animal faeces.

C. perfringens is commonly present in foods and ingredients, occasionally at hundreds per gram. C. botulinum is present less frequently, normally at a few spores per kg. Spores of both C. perfringens and C. botulinum can be eliminated from foods by heating.

C. perfringens
Illness due to C. perfringens occurs after ingestion of large numbers of enterotoxin-producing vegetative cells after food has been temperature-abused, either during cooling after a heat process, or stored unrefrigerated, both of which allow spores to germinate and multiply. Illnesses due to C. perfringens are commonly associated with cooked meat, cooked uncured meat products, the associated gravy, casseroles, or pea soup produced on a large scale, at mass catering in food service establishments, care homes and similar establishments. Almost all outbreaks are the result of cooling slowly, or holding without refrigeration, allowing multiplication of C. perfringens, numbers reaching 106-107 /g, and implying an infective dose of the order 108 of vegetative cells of enterotoxin-producing C. perfringens. Some vegetative cells survive the acid conditions of the stomach and subsequently form spores in the large intestine, at the same time producing enterotoxin. Because the illness lasts only 12-24 h, and the symptoms are usually not serious enough to consult a physician, recorded cases and outbreaks are probably under-reported. Occasionally death occurs, usually in elderly patients. The enterotoxin of C. perfringens is heat labile, heating at 60°C for 5 min destroying the biological activity.

The most essential measures to prevent foodborne diseases caused by C. perfringens are: appropriate cooking, cooling rapidly through the temperature range 55°C to 15°C, holding foods at temperatures <10°-12°C, and re-heating the product to an internal temperature of 72°C before consumption.

Microbiological testing for C. perfringens has limited value in ensuring food safety, because the organism is so common in or on foods that a positive result means little, unless very high numbers are present. Moreover, cultural methods detect all C. perfringens, while enterotoxin is produced by only a fraction of strains.

C. botulinum
Botulism occurs after ingestion of a neurotoxin formed when spores of C. botulinum type A, B, E or F germinate and multiply in a food. It has even resulted after a person, suspecting a food might be spoiled, merely tasted the food after dipping one finger into it. Hence, any multiplication of C. botulinum in foods must be prevented. The toxins of C. botulinum are relatively sensitive to heat and are inactivated by heating at 80°C for 10 min or an equivalent process.

Consumption of a raw product that is contaminated with spores of C. botulinum does not cause botulism. Germination and multiplication of C. botulinum, accompanied by neurotoxin production, must occur before the food is consumed. Outbreaks occur after failures in formulation (recipe) or the process applied, or lack of temperature control in one of the many steps before consumption. Botulism from commercially prepared food is usually associated with a failure of the process, or of container/pack integrity. Historically a high percentage of botulism outbreaks have been associated with home-preserved foods. Those who practise home preservation should be advised of the risks from C. botulinum, should follow well-established practices and procedures, and should not deviate from those procedures e.g. pack size and heating process. Thorough reheating before consumption would inactivate preformed botulinal neurotoxin (BoNT).

Outbreaks have also been traced to small-scale manufacture of “home-made” style foods, where technological knowledge and support may be weak.
Botulism is also associated with traditional fermented fish products that are eaten without heating.

C. botulinum is able to multiply in a very wide range of foods if the temperature is suitable. It is unable to multiply in some fruits because of the low pH value (< 4.5).
Spores of C. botulinum Group I (proteolytic) survive all but the most severe heat process e.g. that applied to low acid canned foods (121°C for 3 min). Spores of C. botulinum Group II (non-proteolytic) are less heat resistant and are inactivated by heating at 90°C for 10 min, or by equivalent processes. Spores that survive heating, or those present on foods that are not heated, are prevented from growing by the pH and/or water activity of the food, preservatives, and the temperature and time of storage.

Laboratory detection methods for C. botulinum are not suited to routine food microbiology laboratories because it is necessary to test for the neurotoxin, and special safety precautions are necessary. Hence, testing for C. botulinum and its toxins is not recommended. Good Hygienic Practices and Good Manufacturing Practices should be built into control of the process, with particular attention paid to the formulation (recipe), the heating process, the storage temperature and the intended duration of storage.

Clostridium perfringens