These organisms can multiply profusely in certain foods without necessarily altering the food organoleptically (that is, in appearance, taste or smell).
In most instances, food poisoning outbreaks result from lack of understanding of food hygiene in the preparation, cooking and care of food, e.g. raw meats placed next to cooked foods.
Bacterial food poisoning is mainly caused either by:
(a) infection - the ingestion of food contaminated with pathogenic organisms (in some cases very low numbers can cause illness)
(b) intoxication - the ingestion of a toxin produced within the food by bacteria prior to consumption.
There are also some organisms which produce a toxin once they are in the intestine.
Campylobacter
Salmonella
Shigella
Vibrio
Yersinia
Listeria
These bacteria can be present in a range of foods including: milk and dairy products, poultry, meat, eggs and vegetables; however, they are not very resistant to heat, i.e. are reduced by at least 6 log reductions after heating at 70°C for 2 minutes.
Some bacteria can cause food poisoning by both infection and intoxication, it is the effects of the toxin which are more severe to the patient.
Escherichia coli (infection and toxin)
Clostridium perfringens (toxin formed in intestine)
The cells of E. coli can be effectively removed by mild heating as above. However, the cells of C. perfringens can develop into spores which are considerably more heat resistant and can survive heating at temperatures as high as 121°C.
Clostridium botulinum
This organism can produce a lethal neurotoxin and is therefore one of the most respected organisms in the food industry; all aspects of food design have to take account of this organism.
Staphylococcus aureus
This organism can produce a very heat stable toxin which remains in the food after all trace of the organism has gone; i.e. no detectable numbers of the organism may be found during microbiological examination.
Bacillus cereus
This organism can produce both very heat resistant spores and very heat stable toxins.
The duration of illness can be short (from one to three days), but cases can be longer. Clinical details, incubation periods and information about the foods eaten, the ingredients used and the way in which they were cooked are very important in determining the cause of an outbreak and towards taking steps to ensure it is not repeated.
The key stages to preventing food poisoning are therefore :
Overall product stability relies on good design, control of ingredients and effective performance of the scheduled process.
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