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Toolbox  –  Understand


What are antibiotics?

Antibiotics are important medicines for the treatment of bacterial infections in humans and animals. Since their introduction in the 1940’s, antibiotics have saved countless lives and have made many medical procedures possible or safer.

Figure 1. The importance of antibiotics. Antibiotics are used to treat many common infections and save the lives of those at high risk for developing severe infections, such as patients undergoing organ transplantation or cancer treatment.

Difference between antimicrobials and antibiotics

There are many different compounds that can inhibit the growth of microorganisms. ‘Antimicrobials‘, ‘antibacterials’ and ‘antibiotics’ are commonly used terms to define these compounds and often they are used interchangeably, but there are important differences between these words:

  • Antimicrobials is a wider term that includes all agents that act against microorganisms, namely bacteria, fungi, viruses and protozoa.
  • Antibacterials act only on bacteria. This term broadly defines all compounds that act against bacteria, including antibiotics. Today the term is sometimes used for different types of disinfectants that are not used as medicine, such as alcohol or triclosan.
  • Antibiotics are produced naturally by microorganisms and kill or inhibit the growth of other microorganisms, mainly bacteria. The word comes from the Greek words ‘anti’, meaning ‘against’, and ‘biotikos’, meaning ‘concerning life’. Strictly speaking, antibiotics do not include agents that are produced by chemical or biochemical synthesis. However for simplicity, synthetic or semi-synthetic variants (such as quinolones) are usually included under the term antibiotics. In this Toolbox, the term antibiotic is used for naturally produced and synthetic compounds that are active against bacteria, mainly those that have been approved for treatment of bacterial infections in humans and/or animals.
Summary diagram of the different types of antimicrobials and their activity: antibiotics, antivirals, antiparasitic agents and antifungals.
Figure 2. Different types of antimicrobials and the microorganisms they are active against.

Antibiotics act on bacteria, not viruses

Antibiotics are mainly active against bacteria, but can also have activity against for example some parasites. They do not cure infections caused by viruses. Below are some examples of bacterial and viral infections:

Bacterial infections Viral infections (antibiotics do not work!)
Bacterial pneumonia Colds
Sepsis (bloodstream infections) Coronavirus disease (COVID-19)
Wound and bacterial skin infections Influenza (the flu)
Urinary tract infections Viral gastroenteritis
Bacterial tonsillitis (strep throat) Measles