Antibiotics

Antibiotics act selectively on bacteria, interfering with their vital mechanisms (formation of the bacterial wall, protein synthesis, etc.) and by causing the death of the bacteria or by blocking their proliferation; in this way, they help the immune system (antibodies, etc.) to heal the infected organism.

The most commonly used antibiotics kill bacteria by acting on structures (e.g. the cell wall) that are missing or are different with respect to human cells, which is why they are not harmed by the drug.

Over the years, antibiotic misuse (self-treating, spontaneous interruption of treatment or administration of inadequate doses), has promoted the development of antibiotic resistance, i.e. the phenomenon by which the bacterium is resistant.
Which is why it is essential to only take antibiotics if you actually need them, with a prescription, being sure to take them at the correct time and use the right methods of administration.