Allgemeines zu Mikro­organismen

General information on microorganisms

Microorganisms: occurrence, significance and influencing factors

Microorganisms are tiny organisms that are invisible to the eye but are found everywhere: in water, in the soil, in the air, on or in living and dead organisms, etc.

Most microorganisms are very useful, as these examples show:

  • The humus formed by microorganisms is a valuable nutrient for plants.
  • The microorganisms present in water convert waste into useful substances.
  • Human and animal digestion requires a diverse range of bacteria.
  • Many foodstuffs, luxury foods and medicinal products are produced by microbial metabolism, e.g. cheese, yoghurt, bread, wine, vinegar.

Pathogenic microorganisms, infection and contamination

The majority of microorganisms are harmless to our health. However, a small proportion of them can cause disease; such microorganisms are referred to as “pathogenic”. If these pathogenic microorganisms cause a disease, this process is called an “infection”. If the pathogenic microorganisms get onto food or objects, this process is called “contamination”.

The different types of microorganisms

Microorganisms are divided into the following four groups:

  • Bacteria, e.g. staphylococci, enterobacteria, pseudomonads
  • Fungi, e.g. mold, filamentous fungi and shoot fungi
  • Parasites, e.g. helminths (worms), protozoa (amoebae, lamblia)
  • Viruses, e.g. influenza, noro and hepatitis viruses

The size of microorganisms varies greatly: the smallest viruses are only about a hundred-thousandth of a millimeter in size, while parasites can grow to around 1 millimeter.

It goes without saying that microbial contamination is undesirable, as it can often have a harmful effect. Therefore, microorganisms that signal a certain type of contamination of the food or sample location are sought.

Bacteria or fungi that indicate such risks or hygiene gaps are referred to as “indicator germs”, and are an important indicator for food hygiene and environmental hygiene:

  • Total bacterial count (TBC) = sum of all bacteria and fungi detected

The total microbial count (TBC) indicates how many aerobic, mesophilic, microorganism colonies (bacteria, fungi) form on an agar culture medium (contact test) over the course of 48 hours of incubation.

The influence of external factors on microorganisms

Three factors influence the occurrence and multiplication of microorganisms:

  • Personal hygiene and personal hygiene behavior, e.g. hand hygiene, clothing, behavior in the event of illness
  • Handling of food, e.g. clean zone / unclean zone, wet zone / dry zone, temperature, shelf life, separation of raw and cooked food
  • Room hygiene, cleaning and disinfection, e.g. waiting rooms, examination rooms, cafeteria, wet zones, etc.

The influence of temperature on microorganisms

In nature and in the natural cycle, microorganisms are present on most foods to a greater or lesser extent. They cover their nutrient requirements directly with these easily utilizable sources of carbon and nitrogen. In addition to chemical and physical influences, temperature is the most important external factor affecting the life, survival and reproduction of microbes.

Cold

Cold does not usually kill microorganisms, but only inhibits their multiplication. After thawing or warming, growth - and thus also reproduction - continues.

Moderate heat

Moderate heat promotes the growth of microbes. Most microorganisms multiply fastest between +20°C and +40°C. Under optimal conditions, bacteria such as “Escherichia coli” double in size every 20 minutes. A simple calculation shows that in this way a single “E. coli bacterium” can produce over 16 million offspring within eight hours.

Heat

From around +62°C upwards, i.e. through sterilization, cooking etc., most bacteria are inactivated and killed. However, some types of spores can survive this heat treatment and are only definitively destroyed at +134°C.

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