Each time that antibiotics are used, the subset of bacteria able to endure their onslaught not only survive but can make the most of the elimination of susceptible bacteria around them to thrive.
Taking antibiotics leads to resistance
Every time antibiotics are taken, bacteria can develop resistance. It is therefore essential that you take these medications correctly and follow your doctor’s advice carefully. This can also help prevent possible relapses.
Antibiotic resistance is a natural phenomenon which has been around for millions of years. Indeed, bacteria and fungi produce antibiotics naturally, to protect themselves. The first antibiotics used in medicine, including penicillin, were extracted from fungi. However, the use of large quantities of such substances in human and veterinary health care since the mid-1940s has greatly amplified a natural process: each time that an antibiotic is used, resistant bacteria multiply and then prosper because they are the only ones able to do so under those particular circumstances.
When bacteria multiply – most are able to do this several times per hour – they must replicate all their genes (DNA). As these copies are made, the bacteria are also subject to errors, known as mutations, some of which might help them survive the onslaught of an antibiotic in their surroundings. They can also acquire this ability by receiving small pieces of DNA (plasmids) from other bacteria – which may or not be of the same species.
Before the antibiotic treatment begins, the resistant bacteria (shown in red) are in the minority.
1) The first antibiotic dose reduces the numbers of non-resistant bacteria. This provides more space for the resistant bacteria, which can multiply.
2) In the course of an antibiotic treatment, mutations – random variations in the bacteria’s genetic material – may also occur, producing bacteria with a new kind of resistance (shown in orange).
3) and 4) As the treatment progresses, it favours the development of the resistant bacteria.
How do bacteria resist antibiotics?
Bacteria can resist antibiotics in several ways:
- By ejecting the antibiotic out of the cell
- By making their membrane impermeable for the antibiotic
- By modifying the antibiotic chemically, to deactivate it
- By modifying the proteins in the cell that are targeted by the antibiotic.
Perhaps the most worrying aspect of the expanding problem of antibiotic resistance – which is advancing world-wide – is the accumulation of several forms of resistance in the same disease-causing bacteria. These multi-resistant bacteria are able to grow normally even when they are treated by several classes of antibiotic at the same time. Some are even able to resist all known antibiotics – this is known as pan-resistance.
Last modification 14.03.2025
Contact
Federal Office of Public Health FOPH
Communicable Diseases Division
Infection Control and Control Measures Section
Schwarzenburgstrasse 157
3003
Bern
Switzerland
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