What are bacteria?

Bacteria are single-celled organisms without a cell nucleus that self-sufficiently produce everything they need to live. In addition, bacteria have their own metabolism and genetic material. They can be between 0.1 and 700 micrometres in size, making them much larger than viruses and yet still smaller than human cells. Under the microscope, bacteria can sometimes have branched filaments, cylindrical structures, a rod or spherical shape.

Contrary to the misconception that all bacteria cause infectious diseases, many bacteria are actually useful. For example, humans naturally have many bacteria in the intestines, in the oral cavity and on the skin, without these causing diseases. On the contrary: "good" bacteria help the intestines with digestion, for example. On the skin, the so-called "good" bacteria ensure that disease-causing germs do not spread there. Only about one percent of all bacteria are important pathogens of infectious diseases, for example when they invade the body and produce metabolic products there. The best-known bacterial diseases include chlamydia, diphtheria, whooping cough, listeriosis, plague, salmonella, tetanus, gonorrhoea, tuberculosis and typhoid. There are already vaccinations against some of these diseases. As a rule, bacterial infections are treated with antibiotics.

How are bacteria constructed?

Similar to a plant cell, a bacterial cell also has a cell wall, which is made of murein. While some bacteria have only one layer of murein in their cell wall, others have several layers of murein. This difference in the structure of the cell wall causes bacteria to take on a different colouring in the so-called Gram staining method. Still other bacteria surround themselves with a capsule in addition to a cell wall. This is a very dense protective layer consisting of sugars and protein building blocks (so-called amino acids). In addition to the capsule, a so-called biofilm also offers protection. This is a sticky substance that bacteria secrete to attach themselves to other cells or objects. Especially on the teeth, caries bacteria (plaque) can form thanks to this biofilm.

There are also a few bacteria that have no cell wall at all, such as mycoplasma and thermoplasma species. Mycoplasmas are parasitic bacteria that can reproduce themselves. The so-called thermoplasma species, on the other hand, are heat-loving bacteria that have a stable plasma membrane and are found primarily in volcanic soils.

How do bacteria develop?

Bacteria are, so to speak, the oldest inhabitants of the earth and reproduce under the most diverse conditions by cell division. In the process, the bacterium divides its cell into two parts and thus practically clones itself. Bacteria are not only found in the air, but also in water or food and can survive for a very long time in the environment or even in the human body.

How can bacteria be killed?

Bacteria react sensitively to high temperatures, but also to chemical substances such as alcohol, aldehydes and/or chlorine. For the medical treatment of bacteria in the human body, for example, an antibiotic is used. The antibiotic either prevents bacteria from multiplying or destroys them in a direct way. On the one hand, the antibiotic can ensure that the bacteria cannot build a new cell wall after cell division. Since the cell wall acts as a protective outer shell, the bacterium bursts without this cell wall and dies. On the other hand, the antibiotic can also block protein biosynthesis and thus kill the bacterium.

Are all bacteria the same?

There are some bacteria that are true survival artists. Not only can they withstand extreme cold, heat or drought, some of them can even survive without any oxygen at all. In very poor living conditions, some types of bacteria can also form spores, which makes them insensitive to heat, radiation and/or desiccation.

Still other bacteria are extremely mobile or quite sturdily built, i.e. they are surrounded by a membrane from the outside and additionally protected by a cell wall. Most bacteria have a shell of sugar building blocks (biofilms) that protects them from the environment.

In general, bacteria can be classified according to their respective colour, which they take on when they come into contact with certain colouring agents. This is known as Gram staining, which can be differentiated as follows:

• Gram-positive bacteria: such as the diphtheria or anthrax pathogens, as well as the pneumococci and streptococci, which cause pneumonia and tonsillitis, among other things. Gram-positive bacteria turn blue.
• Gram-negative bacteria: such as the pathogens of cholera, whooping cough, plague and typhoid fever. The Gram-negative bacteria turn red.

What do the different forms tell us about bacteria?

Generally, the three different forms of bacteria are distinguished:

• spherical bacteria: This includes all roundish to oval bacteria, the so-called cocci. They usually form typical groups of two, four or eight, come together in larger clusters (staphylococci) or form more or less long chains (streptococci).
• rod-shaped bacteria: The so-called rod-shaped bacteria can occur individually (such as the typhoid bacteria) or form different clusters, such as the diphtheria bacteria. If the rod-shaped bacteria need oxygen to live and form spores, they are also called bacilli, such as the anthrax bacteria.
• helical bacteria: are again divided into four groups: the spirillae, borrelia, treponemen as well as leptospires.

What diseases can bacteria cause?

There are a variety of bacteria that can cause the following diseases, for example:

• Chlamydia: doctors distinguish between different types of chlamydia, each of which can cause different clinical pictures, such as conjunctivitis, an infection of the urinary and/or genital organs, and pneumonia.
• Diphtheria: manifests itself through a barking cough, difficulty swallowing and/or a sweet-smelling, foul-smelling mouth odour. These symptoms are triggered by the toxin of the gram-positive rod bacterium Corynebacterium diphtheriae.
• Gonorrhoea is a sexually transmitted disease caused by Neisseria bacteria. If the disease is treated early, it usually heals completely. If it is diagnosed and treated later, infertility may remain as a late consequence.
• Whooping cough: is actually a children's disease, which can also increasingly affect adolescents and adults and is usually caused by the gram-negative bacterium Bordetella pertussis.
• Meningococci: can cause meningitis or bacterial blood poisoning (sepsis).
• Pneumococci: also belong to the streptococci, but they usually occur in pairs (diplococci). Pneumococci can cause pneumonia, but also meningitis, middle ear and/or sinusitis.
• Salmonella: cause a typical foodborne illness (salmonellosis).
• Scarlet fever: are caused by the gram-positive, spherical A streptococci (Streptococcus pyogenes).
• Staphylococci: can cause abscesses, wound infections or bacterial blood poisoning (sepsis). Staphylococcus aureus strains are particularly feared because they are resistant to methicillin and other antibiotics.
• Streptococci: So-called A streptococci can cause middle ear and/or tonsillitis, erysipelas, pneumonia and/or rheumatic fever. B-streptococci can cause meningitis. Other streptococci can appear as caries bacteria.
• Tetanus (lockjaw): is caused by bacteria of the Clostridium tetani type. The disease causes severe muscle cramps, which can lead to death by suffocation.
• Tuberculosis: is mostly caused by the pathogen Mycobacterium tuberculosis.