Antibiotic

If a filter-paper disc containing an antiseptic or antibiotic is placed on the agar, the substance diffuses outwards. Where enough of it prevents bacterial growth, a clear zone of inhibition appears around the disc. Comparing these zones lets you investigate how different treatments affect the bacteria on the plate.

Antibiotics are medicines used to treat bacterial infections. Some kill bacterial cells, while others stop them growing or reproducing. If the bacteria are killed or their population cannot increase, the infection can be brought under control.

Antibiotics and antivirals are used to treat particular kinds of infection, while antiseptics help prevent microorganisms entering tissues through places such as cuts.

For example, an effective antibiotic acts on susceptible bacteria causing an infection. Other medicines mainly control symptoms: a painkiller may reduce pain or fever without killing the pathogen responsible. A medicine may therefore shorten an illness, make its symptoms less severe, eliminate its cause, or combine some of these effects.