An antibiotic is something that stops bacteria and fungal growth or kills bacteria and fungi.

Antibiotics are different from disinfectants, which are weaker at destroying microbes.

The first antibiotics were extracts of natural substances that living things produce to counter an attack by bacteria or fungi. Nowadays people know how to make them without having to extract them.

Penicillin is a good example of an antibiotic. It is produced by the Penicillium fungi. Sulphonamides are examples of substances made as chemicals.

Microbes can get used to antibiotics and adapt to defend themselves against them. That is why it is so important to use antibiotics sparingly.