Micro-organisms – a brief introduction
Micro-organisms – a very small life form such as bacteria, viruses, some fungi and microscopic viruses. not all bacteria are harmful. There are three main types: helpful bacteria, pathogenic bacteria and spoilage bacteria.
Helpful Bacteria & Micro-organisms
Helpful bacteria sometimes called ‘friendly’ bacteria. these can be essential for example breaking down decaying matter. There are the probiotics, which are supposed to assist with the promotion of good health.
Pathogenic bacteria are disease producing organisms, they cause illness and food poisoning. Food poisoning bacteria produce toxins (poisons). They cannot be detected by visual inspection, the toxins they produce may be either exotoxin or endotoxins. Cooking temperatures of approximately 70°C for two minutes or higher temperatures normally destroys bacteria, however, the number of bacteria present and the type of food also effect the time needed to kill bacteria. Toxins and spores produced by some food poisoning bacteria are not affected by high temperatures, an example would be Clostridium Botulinum (toxin in food) which requires 121°C for three minutes.
Spoilage bacteria are micro-organisms too small to be seen without a microscope that cause food to deteriorate and develop unpleasant odours, tastes, and textures. These one-celled micro-organisms can cause fruits and vegetables to get mushy or slimy, or meat to develop a bad odour.
Spores are the protective form of some bacteria. The spore allows them to survive adverse conditions such as drying, freezing, dehydration and cooking. They cannot be detected by visual inspection and they can survive normal cooking and can germinate during slow cooling. Temperatures in excess of 100°C are required for long periods to destroy spores.
Moulds are aerobic chlorophyll-free fungi which produce filaments and form a branched network of mycelium. Moulds will grow on most foods, whether, moist, dry acid or alkaline, high in salt and sugar concentrations. high humidity and fluctuating temperatures will accelerate mould growth.
Yeasts are microscopic fungi which reproduce by budding. They grow best in an oxygen environment, but fermentative types will grow without oxygen, but very slowly. Most yeasts prefer acid foods pH 4 to 4.5 with reasonable levels of moisture. They will also grow in high levels of salt and sugar.
Yeasts are used in the manufacture of bread, beer and vinegar. Yeasts are responsible for causing spoilage to many foods including, jam, fruit juice, honey, meats and wines.
Viruses are smaller than bacteria, they do not benefit from food, but do multiply in cells. Viruses are responsible for illnesses such as viral gastroenteritis and hepatitis A.
Protozoa live in most habitats such as oceans, soil and decaying matter. Some are pathogenic and cause waterborne outbreaks. They do not benefit from food, but use food as a vehicle. However, there cysts may remain infectious in food for a long time. Protozoa are a low dose organism, which means, few are required to cause illness. There are two main types in the UK. Cryptosporidium parvum and Giardia lamblia.
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