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How antibiotics work

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Antibiotics are chemicals that disrupt and kill bacteria.

Note that they don’t kill viruses, fungi, or parasites.

For example, influenza (“the flu”) is a virus, not a bacteria. Therefore antibiotics can’t help fight the influenza virus.


Antibiotics work by blocking vital processes in bacteria, killing the bacteria or stopping them from multiplying.

This helps the body’s natural immune system to fight the infection.

Different antibiotics work against different types of bacteria.

  • Antibiotics that affect a wide range of bacteria are called broad spectrum antibiotics (eg, amoxicillin and gentamicin).

  • Antibiotics that affect only a few types of bacteria are called narrow spectrum antibiotics (eg, penicillin).

Different types of antibiotics work in different ways.

For example, penicillin destroys bacterial cell walls, while other antibiotics can affect the way the bacterial cell works.

Doctors choose an antibiotic according to the bacteria that usually cause a particular infection.

Sometimes your doctor will do a test to identify the exact type of bacteria causing your infection and its sensitivity to particular antibiotics.

Antibiotic medicines may contain one or more active ingredients and be available under different brand names. The medicine label should tell you the active ingredient and the brand name.

_ from NPS MedicineWise, Australian Govt. Dept. of Health

Simple animation showing how an antibiotic disrupts the building of a cell wall.

Once the cell wall is disrupted, water can enter, making the cell swell, and eventually burst.

antibiotic cell wall

Image from Waterborne Diseases: Typhoid, By Olivia W.


Ways that antibiotics can disrupt bacteria

You can right-click on each image to expand it,  or click here for the original page.  It shows us several different types of antibiotics. Each has a different way of disrupting a bacteria,

This image is from “Mechanisms of  Bacterial Resistance to Aminoglycoside Antibiotics”, 2019 RCSB PDB Video Challenge for High School Students. from the PDB-101 website. This is an educational portal of the RCSB PDM (protein data bank.)

Mechanisms of antibiotics


Mechanisms of antibiotics 2


Related content

What is an antibiotic? Form Learn.Genetics, Univ. of Utah

Learning Standards

MassachusettsComprehensive Health

8.1 Describe how the body fights germs and disease naturally and with medicines and

8.5 Identify ways individuals can reduce risk factors related to communicable and chronic diseases
8.6 Describe the importance of early detection in preventing the progression of disease

8.7 Explain the need to follow prescribed health care procedures given by parents and health care providers

8.13 Explain how the immune system functions to prevent and combat disease

8.19 Explain the prevention and control of common communicable infestations, diseases, and infections

Benchmarks for Science Education, AAAS

Inoculations use weakened germs (or parts of them) to stimulate the body’s immune system to react. This reaction prepares the body to fight subsequent invasions by actual germs of that type. Some inoculations last for life. 8F/H4

If the body’s immune system cannot suppress a bacterial infection, an antibacterial drug may be effective—at least against the types of bacteria it was designed to combat. Less is known about the treatment of viral infections, especially the common cold. However, more recently, useful antiviral drugs have been developed for several major kinds of viral infections, including drugs to fight HIV, the virus that causes AIDS. 8F/M6** (SFAA)

Pasteur found that infection by disease organisms (germs) caused the body to build up an immunity against subsequent infection by the same organisms. He then produced vaccines that would induce the body to build immunity to a disease without actually causing the disease itself. 10I/M3*

Investigations of the germ theory by Pasteur, Koch, and others in the 19th century firmly established the modern idea that many diseases are caused by microorganisms. Acceptance of the germ theory has led to changes in health practices. 10I/M4*

Current health practices emphasize sanitation, the safe handling of food and water, the pasteurization of milk, isolation, and aseptic surgical techniques to keep germs out of the body; vaccinations to strengthen the body’s immune system against subsequent infection by the same kind of microorganisms; and antibiotics and other chemicals and processes to destroy microorganisms. 10I/M7** (BSL)

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