Foodborne diseases / Clostridium perfringens
Clostridium perfringensClostridium perfringens is widely distributed in nature and is common in the gastrointestinal tract of man and food animals. Being a spore-forming organism, it may survive normal cooking of food and then multiply to hazardous levels if temperature control is inadequate.
1. Bacteriological characteristics
Cl. perfringens is a Gram-positive, anaerobic, spore-forming, rod shaped bacterium which is member of the family Bacillaceae. Various toxins are elaborated by the organism and these are used to subdivide the species into five principal types, A-E. Only types A and C produce the enterotoxin that is associated with food poisoning.
2. Disease in humans
Food poisoning is an intoxication which develops within 6-24 hours of ingesting food in which Cl. perfringens has grown. The illness is characterised by abdominal pain, diarrhoea and nausea. These symptoms are due to enterotoxin produced in the intestinal tract during sporulation. The condition is self-limiting and recovery usually occurs without treatment within 1-2 days.
3. Sources of infection and epidemiology
The organism is widely distributed in soil, dust, vegetation and insects and is also found in the gastrointestinal tract of most warm blooded animals. It is commonly present on raw meat. Contamination of meat-containing foods may originate from the meat itself or the handling environment of the kitchen.
In the slaughterhouse, there are instances where Cl. perfringens may be introduced into the spinal cord on the pithing rod. This can lead to rapid deterioration of the meat during the initial stages of chilling and before an inhibitory temperature is reached. The risk i greatest in carcasses where the pH value of the meat is higher than usual.
The organisms grows particularly well in red meat and poultry that have been cooked slowly at relatively low temperatures or stored under poor refrigeration and then consumed without thorough reheating.
4. Growth properties in relation to meat and meat products
Cl. perfringens is less sensitive to oxygen than many clostridia and is able to grow under conditions that are not strictly anaerobic. The spores vary in heat resistance and those that are more resistant are most likely to survive conventional cooking of contaminated foods such as meat. Subsequent outgrowth and multiplication of vegetative cells may be favoured by inadequate storage conditions. However, the vegetative cells are highly sensitive to freezing.
Growth occurs at temperatures between 12-50°C and is extremely rapid at 43-47°C. the growth rate is much less at 15-20°C. The minimum pH value for growth is 5.5-5.8 and the minimum water activity value is 0.93. Good growth is observed in the presence of 5-8% NaCl.
It is rarely necessary to use enrichment methods for recovering Cl. perfringens from suspect cooked foods. Various media have been described and these contain antibiotics to inhibit competing organisms. The media used include tryptose-sulphite-cycloserine (TSC) agar, with and without egg yolk, and oleandomycin-polymixin-sulphadiazine-perfringens (OPSP) agar.
6. Control measures in slaughterhouses and cutting plants
Cl. perfringens may be isolated in small numbers from raw red meat and poultry meat. The level of contamination reflects, in part, the standard of slaughterhouse hygiene. It is the control of faecal contamination in general and prompt cooling of carcasses that reduce risk from this organism. Survival in cooked meats poses the greatest risk, since rapid growth can occur during cooling. Prompt cooling and suitable storage temperatures for the cooked product are a pre-requisite for controlling growth of the organism in this situation.