What are microbes?

Microbes are tiny forms of life that surround us – too small to be seen by the naked eye. They are found in water, in the soil, and in the air. Our body is also home to millions of these microbes, also called microorganisms. Some microbes make us sick, others are important for our health. The most common are bacteria, viruses and fungi. There are also microbes from the group of protozoa. These are tiny living creatures that are responsible for diseases such as toxoplasmosis and malaria.

Bacteria are made up of just one cell

Bacteria are single-cell organisms. Under the microscope they look like little balls, rods or spirals. Some bacteria need oxygen to survive and others do not. Some love the heat, while others prefer a cold environment. Well-known bacteria include for instance salmonella and staphylococci.

Most bacteria are not dangerous for human beings. Many of them even live on or in our body and help us to stay healthy. For instance, lactic acid bacteria in the bowel support digestion. Other bacteria help the immune system by fighting germs. Some bacteria are also needed in order to produce certain types of food, for example yoghurt, sauerkraut or cheese.

Less than 1% of all bacteria are responsible for diseases like tuberculosis or urinary tract infections. Many other infections can also be caused by bacteria - including diarrhea, inflammations of the lungs or tonsillitis – but all of these diseases can also be caused by other types of germs.

Bacterial infections can be treated with antibiotics. These are medicines that stop bacteria from multiplying or that kill the bacteria. You can find more information about the correct use of antibiotics here.

Viruses invade healthy cells and make us sick

In contrast to bacteria, viruses have no cells of their own. This means that they are also not living organisms in the stricter sense. They are instead made up of one or more molecules, inside of a protein shell. The genetic information found inside of this shell is needed for the viruses to reproduce. Viruses can appear in quite different ways: for example, circular, rod-like or even tadpole-shaped.

Many viruses are responsible for diseases. Some are harmless and only trigger a bothersome cold, while others can cause serious diseases like HIV/AIDS. Other diseases caused by viruses include influenza, measles or inflammation of the liver (viral hepatitis).

Viruses invade healthy cells and start to multiply from these cells. Without these host cells, a virus cannot reproduce. Not all viruses cause symptoms and in many cases the body successfully fights back against the attackers. This is the case with cold sores, which many people have experienced at some time. They are caused by viruses that are found in certain nerve cells and can lead to lip blisters in some people. Most of these end up healing by themselves.

It is relatively difficult to fight viruses with medication. To protect against some viruses the immune system can be “trained” by a vaccination so that the body is made less sensitive to the virus.

Fungi are plants

Fungi are plants, strictly speaking. The best-known fungi include yeast, mold and edible fungi like mushrooms. Just like bacteria, some fungi naturally occur on the skin or in the body. But fungi can also cause diseases.

Diseases caused by fungi are called mycoses. These include the common athlete’s foot or fungal infection of the nails, for example. Fungal infections can sometimes also cause inflammations of the lungs or mucous membranes in the mouth or on the reproductive organs, and become life-threatening for people who have a weakened immune system. But human beings have also profited from the beneficial qualities of some fungi. We owe the discovery of penicillin to a mold that can be used to produce this antibiotic.

Fungal infections can be treated with drugs that are called antimycotics. They kill the fungi or prevent them from being able to multiply.

Not all germs are highly contagious – but you can catch some of them relatively quickly. These especially include viruses that cause respiratory tract infections, like colds or the flu. You can find out how to protect yourself from respiratory viruses here.

Author: Institute for Quality and Efficiency in Health Care (IQWiG)

© IQWiG (Institute for Quality and Efficiency in Health Care) Last update of this website: 05/22/2012