Antibiotics

Bild von Penicillium

The term “antibiotic” (Paul Vuillemin 1889) is derived from antibiosis (from Greek “anti” = against, and “bios” = life). Antibiotics are metabolites of low molecular weight produced by moulds or bacteria that are able to inhibit the growth of other microorganisms at low levels (=bacteriostatic) or even kill them (=bactericides). Antibiotics are used as medicines to treat infectious diseases caused by bacteria. We differentiate between naturally and synthetically produced antibiotics. Most of the antibiotics sold today are derived from natural substances, primarily from fungi and bacteria.

The best known, natural antibiotic is Penicillin. Alexander Fleming discovered the effects of substances found in the Penicillium mould on bacteria in 1928. However, it took many years for the active agent to be produced in sufficiently high quantities for it to be used as a medicine.
French military physician Ernest Duchesne had already described his observation on the effect of moulds on bacteria in his thesis 30 years earlier. However, the Pasteur Institute rejected his thesis at the time. It was only in 1949, four years after Alexander Fleming had been awarded the Nobel Prize, that Duchesne was posthumously honoured for his achievements by the French Académie de Médecine.

Arsphenamine was synthetically produced and introduced by Paul Ehrlich in 1910 and is considered the first antibiotic discovered in history. It is a narrow spectrum antibiotic and was used as an effective and relatively harmless treatment for the then widespread health problem of syphilis for the first time. Meanwhile, Arsphenamine has been replaced by newer substances in modern medicine. Gerhard Domagk discovered Sulfonamide and introduced it in 1935.  

How Do Antibiotics Work?

The answer to this question is found in the structural difference between bacterial cells and human or animal cells. Antibiotics are built in a way that they can only dock onto bacterial cells, but not onto human or animal cells, working according to the “lock and key” principle. As a result, only bacteria are targeted and destroyed.

Some antibiotics destroy the cell membrane, while others interfere directly with the metabolism of the bacterial cells by limiting their protein production or affecting bacterial chromosomes by preventing the bacterial DNA from uncoiling or the genes from being transcribed.

We differentiate between the following mechanisms: 

  • bacteriostatic: the bacteria are stopped from reproducing
  • bactericidal: the bacteria are killed, but the dead cells remain 
  • bacteriolytic: the bacteria are destroyed, their membrane is dissolved

When Are Antibiotics Used?

Antibiotics are among the most prescribed medications worldwide. They form the largest single segment in total drug consumption with a market share of 13 percent. Antibiotics are also used specifically as part of veterinarian treatment in animal husbandry. Their use as food supplements has been prohibited in the EU since the beginning of 2006.

Why Is There Antibiotic Resistance?

Antibiotic resistance is the resistance developed by strains of bacteria to a specific antibiotic they would naturally be susceptible to. Antibiotic resistance is part of the programmed adaption mechanism existent in each bacterial cell, causing the bacterium to adapt to changes in the environment. Once a bacterium becomes resistant to an antibiotic, the minimum inhibitory concentration (MIC) which originally prevented the growth of the bacterium is not effective anymore and does not prevent the bacterium from growing. It is believed that microorganisms can develop resistances to almost any antibiotic.

How do these mircoorganisms develop this ability?

On the one hand, there are primary resistances, i.e. specific bacteria have natural resistances to specific agents. This is widely known and is taken into account by physicians and veterinarians when treating bacterial infections in humans and animals. However, this phenomenon is also used to identify bacteria. Antibiotics are also used as a selection means in molecular biology. In cloning, the characteristic resistance to a specific antibiotic is used to identify whether a strain carries a specific gene that should be built into the bacterium.

On the other hand, there is secondary resistance, i.e. resistance developed over the course of time. This means that bacteria develop the ability to become resistant to an agent through spontaneous genetic mutation or the acquisition of new genes.

Bacterial resistance is based on several mechanisms:

Many bacteria can break down antibiotics or restructure them in a way that they become ineffective. Penicillin, for instance, is broken down by an enzyme that is formed by bacteria (β-Lactamase).

Other bacteria alter the target structures that are usually attacked by antibiotics, causing the so-called lock and key principle to become ineffective and the antibiotic cannot cause damage to the bacterium anymore. Moreover, antibiotics can be flushed out from cells. This type of resistance can lead to the complete removal of the antibiotic substance from the cell.

Mankind was confronted with resistance development only a few years after beginning to use antibiotics. One reason was the rather careless use of these substances and their indiscriminate use in both human and veterinarian medicine. As a result, antibiotics must be used and administered with due care and a strong sense of responsibility.

Thus, it is important to discuss the prescription of antibiotics with patients in human medicine and only use them if their use is justified and reasonable. Underdosing antibiotics may lead to resistance, so could a too-short period of use – this is where the patient’s own responsibility comes into play.

The use of antibiotics in veterinary medicine is regulated much more tightly now than a few years ago. Performance enhancers are prohibited, the use of drugs is monitored widely on an official level and from a veterinarian perspective via animal health services. Additionally, there are state-run monitoring programmes to keep the risk of antibiotics use and resistance development under control as much as possible.

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