How do antibiotics work?

Antibiotics disrupt essential processes or structures in the bacterial cell. This either kills the bacterium or slows down bacterial growth. Depending on these effects an antibiotic is said to be bactericidal or bacteriostatic.

Bactericidal and bacteriostatic antibiotics

A bactericidal antibiotic kills the bacteria while the bacteriostatic antibiotics stop bacterial growth without killing them. The human immune system is then needed to clear the infection.

Antibiotic targets in bacteria

There are several classes of antibiotics with different mechanisms of action and bacterial targets. In principal, there are three main antibiotic targets in bacteria:

1. The cell wall or membranes that surrounds the bacterial cell
2. The machineries that make the nucleic acids DNA and RNA
3. The machinery that produce proteins (the ribosome and associated proteins)

These targets are absent or structurally different in human and mammalian cells, which means that antibiotics usually do not harm our cells. However, antibiotics can in some cases have unpleasant side effects. Read more under Why should I care? – Risks for the individual and society.

Narrow-spectrum and broad-spectrum antibiotics

Antibiotics can either have a narrow or broad spectrum of activity. Narrow-spectrum antibiotics are more specific and are only active against certain groups or strains of bacteria. Broad-spectrum antibiotics instead inhibit a wider range of bacteria. Narrow-spectrum antibiotics are generally preferable since the effect on other non-disease causing bacteria is more limited. Unfortunately, broad-spectrum antibiotics are often used since it can be difficult for doctors to diagnose the infectious agent due to a lack of training and/or available diagnostic tools. For more information, see How did we end up here – Use and inappropriate use – In human medicine.

See also these selected resources for more details on different antibiotics and their mechanisms of action.

Selected Resources