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Bacteria growing on an agar plate

Antibiotic resistance tests: Bacteria are streaked on the dish on which antibiotic impregnated white disks are placed. Bacteria in the culture on the left are susceptible to the antibiotic in each disk, as shown by the dark, clear rings where bacteria have not grown. Those on the right are fully susceptible to only three of the seven antibiotics tested.

An antibiotic (or antibacterial) is a chemical compound that kills bacteria or slows their growth. They are used as medicine to treat and cure diseases caused by bacteria. The first antibiotic discovered was Penicillin, a natural antibiotic produced by a fungus. Production of antibiotics first began in 1939, and in the modern day, they are made by chemical synthesis. Antibiotics can not be used to treat viruses.

Maclyn McCarty explained what it was like before antibiotics:

"There are a number of infections from which no-one had [ever] recovered before the discovery of effective anti-bacterial agents".