In this article we will discuss about the food poisoning that is caused by bacteria and fungi.
Food-Poisoning Caused by Bacteria (Bacterial Food-Intoxications):
There are two major food-poisoning or food-intoxications caused by bacteria.
Botulism and Staphylococcal-poisoning.
Botulism is caused by the ingestion of food containing the neurotoxin (toxin that affects the nervous system) produced by Clostridium botulinum, an anaerobic spore forming bacterium. Sixty to seventy per cent cases of botulism die. There are 7 types (type A, B, C, D, E, F, G) of these neurotoxins recognised on the basis of serological specificity.
The neurotoxin of C. botulinum is a protein. It has been purified and crystallized and is so powerful that only a dose as low as 0.01 mg is said to be fatal to human beings. The toxin is absorbed mostly in the small intestine and paralyzes the involuntary muscles of the body.
The main sources of botulism are canned meat, fish, string beans, sweet corn, beans, and other low medium acid foods. The foods implicated are generally those of a type that have undergone some treatment intended for the preservation of the product such as canning, pickling or smoking, but one which failed to destroy the spores of this bacterium.
When the intended preservative treatment is inadequate and is followed by storage conditions which permit the germination and growth of the microorganisms, one of the most lethal toxins known to humanity is produced. The toxin has been known to persist in foods for long periods, especially when storage has been at low temperatures. It is unstable at pH value above 6.8.
Temperature is considered to be the most important factor in determining whether toxin production will take place and what the rate of production will be. Various strains of C. botulinum types A and B vary in their temperature requirements; a few strains grow at 10 to 11°C. However, the lowest temperature for germination of spores of the most of the strains is 15°C and maximum of 48°C.
Symptoms generally occur within 12 to 36 hours after consumption of the spoiled food. Early symptoms are digestive disturbances followed by nausea, vomiting, diarrhoea together with dizziness and headache. Double vision may occur early and there may be difficulty in speaking.
Mouth may become dry, throat constricted, tongue may get swollen and coated. Involuntary muscles become paralysed and paralysis spreads to the respiratory system and to the heart. Death normally results from respiratory failure.
Canned food should be properly processed by using approved heat processes. Food that has been cooked but not well heated should be avoided. Raw foods and frozen foods thawed and held at room temperature should be avoided. Gassy and spoiled canned foods should be rejected. Boiling of suspected food for at least 15 minutes is required.
Successful treatment is by the administration of polyvalent antitoxin in the early stages of infection. Once the symptoms appear the treatment fails to prove useful.
This is the most common type of food-poisoning caused due to the food contaminated with a potent toxin, namely, enterotoxin. This toxin is produced by certain strains of Staphylococcus aureus. A sudden onset of illness starts usually within 3 to 6 hours after ingestion of the contaminated food.
These bacteria are commonly present on the skin, nose and other parts of human body. People who handle foods carelessly usually transfer them to the food. Foods most commonly contaminated involve those which are eaten cold, e.g., cold meat, poultry, salads, bakery products, etc.
As said earlier, the disease starts within 3 to 6 hours after ingestion of the contaminated food and is manifested by nausea, vomiting, abdominal pain and diarrhoea within 24 to 48 hours. If the case becomes severe, dehydration and collapse may follow. However, in usual conditions death is rare.
The disease can be controlled by preventing the entry of the bacteria to food. It is important that all susceptible foods are kept under refrigeration to restrict the growth of the bacteria and also by the destruction of the bacteria by heat.
Food-Poisoning (Mycointoxications) Caused by Fungi:
Mycotoxins are chemical substances produced by a variety of fungi, e.g., aspergilli, penicilli, Rhizopus, Fusarium spp., and mushrooms (poisonous; called toadstools). The illness that results from the ingestion of foods containing fungal toxins is called ‘mycotoxicosis’. Mycologists have come to discover a number of mycotoxins which have proved extremely harmful, sometimes lethal to animals and human beings.
Important ones are as follows:
Aflatoxins are one of the most potent mycotoxins produced by Aspergillus flavus and related strains. It has been found that about 60% strains of A. flavus produce this toxin. This discovery of aflatoxins is comparatively of recent origin. In 1960, about 100,000 Turkey poults died in England within few months. It was found that the peanut meal fed to them was heavily contaminated with A. flavus.
The chemical substance isolated from such peanut meal was found toxic and was named ‘aflatoxin’. However, some other fungi, e.g., Aspergillus niger, A. oryzae, A. ochraceus, Penicillium citrinum, etc. have also been reported to produce anatoxins. So the name aflatoxin is now generally used for a number of related toxins.
Anatoxins occupy the most important position among mycotoxins because of their potent carcinogenic nature and high frequency of occurrence in nature. More specifically, aflatoxin B1 is one of the most potent aflatoxins. They are responsible for liver cancer in laboratory animals and even human beings.
2. Amatoxins and Phallotoxins:
These two mycotoxins are considered to be produced by the poisonous mushroom Amanita phalloides, the so called death cap. This mushroom is deadly poisonous and almost about 90 to 95% deaths of mushroom-eaters in Europe have been due to eating of this fungus. These two mycotoxins are chemically cyclopeptides.
According to Lincoff and Mitchel (1977) the most potent amatoxins are α-amanitin and β-amanitin while the phalloidin is the most potent phallotoxin. However, studies reveal the fact that these are the amatoxins which are strongly poisonous comparatively, and are responsible for producing hypoglycemia, liver-distrophy and kidney-failure leading to the death of the victim.
This mycotoxin is thought to be present in an edible mushroom, namely, Coprinus atramentanius. This chemical becomes toxic and results in gastrointestinal upsets and other physical discomforts when the mushroom-eating is accompanied with alcohol.
Gyromitrin (monomethylhydrazine) is deadly poisonous mycotoxin reported to be present in the fruiting bodies (basidiomata) of saddle fungi (Helvella spp.) and false morels (Gyromitra spp.). This toxin is water soluble. It is thought that if the fruiting bodies be parboiled two or three times and the liquid discarded, the mushrooms become safe to eat.
Ochratoxin was first isolated from the filtrates of Aspergillus ochraceus and is now produced by a number of Aspergillus and Penicillium spp., with Penicillium verrucosum being the dominating producer.
These mycotoxins represent a group of closely related derivatives of isocoumarin linked to L-phenylalanine, an amino acid, and are reported mainly in temperate area of North America and Europe. Ochratoxins occur mainly in grains but have also been reported in coffee, beans and peanuts, and are toxic to ducklings, chicks and rats.
Trichothecenes are produced by the species of Fusarium, Cephalosporium, Myrothecium, Trichoderma and Stachybotrys. Out of 30 known trichothecenes, T-2 toxin, nivalenol and deoxynivalenol are of common occurrence, and cause a hyperestrogenic syndrome, haemorrhage and sometimes abortion in swine.
This mycotoxin is produced by a number of Fusarium spp., e.g., F. graminearum and F. moniliforme. It occurs predominantly in maize and is similar to trichothecenes in its effects.