Share the article

Antibiotics are drugs used to treat bacterial infections in humans and animals. The word comes from the Greek words ‘anti’, meaning ‘against’, and ‘biotikos’, meaning ‘concerning life’.

Photo: via Pexels

Antibiotics function by interfering with essential processes or structures in the bacterial cell. This either kills the bacterium or slows down bacterial growth. Importantly, antibiotics are not active against viruses. Therefore, they should not be used for viral infections, such as common cold, most upper respiratory infections, the flu, viral gastroenteritis or measles. Further, they have very little additive effects in the treatment of mild bacterial infections including wound infections, bacterial gastroenteritis and throat infections. These infections can often be taken care of by the body´s immune system. However, antibiotics are truly life-saving medicines for patients suffering from severe bacterial infections (e.g. pneumonia, meningitis and sepsis)!

Mechanisms of action

In principal, there are three main antibiotic targets in bacteria:
1. The cell wall that surround the bacterial cell
2. The machineries that synthesize the nucleic acids DNA and RNA
3. The machinery that synthesizes proteins

These targets are absent or different in the cells of humans and other mammals, which means that the antibiotics usually do not harm our cells but are specific for bacteria. However, antibiotics can often have side effects, which is described in the factsheet at the bottom of this page.

Antibiotic classes

Antibiotics are grouped into different classes. For example, the beta-lactam group includes multiple substances with common core molecule and similar mechanism of action. The beta-lactams are further sub-grouped into penicillins, cephalosporins, carbapenems and monobactams, comprising many commonly used antibiotics. Other important antibiotic classes include the fluoroquinolones, aminoglycosides, tetracyclines and glycopeptides.

Narrow-spectrum vs. broad-spectrum antibiotics

Antibiotics can either have a narrow or broad spectrum of activity. Narrow-spectrum antibiotics are more specific in that they are only active against certain groups or species of bacteria. Broad-spectrum antibiotics inhibit a wider range of bacteria, which also results in a more pronounced effect on the bacterial normal flora. Therefore, narrow-spectrum antibiotics should be prescribed when possible to reduce the risk for side effects and selection of resistant bacteria. However, broad-spectrum agents are needed in the treatment of severe infections where the infecting pathogen is unknown and inappropriate therapy will result in a high risk for complications or even mortality.

Find out more

Here is a link to a factsheet by Compound Interest: Different classes of antibiotics: An overview

© Uppsala University