Antibiotics or antibacterials are a type of antimicrobial used specifically against bacteria, and are often used in medical treatment of bacterial infections. They may either kill or inhibit the growth of bacteria. Several antibiotic agents are also effective against a number of fungi, protozoans and some are toxic to humans and animals, even when given in therapeutic dosage. They are not effective against viruses such as the common cold or influenza, and may be harmful when taken inappropriately.
Antibiotics revolutionized medicine in the 20th century, and have together with vaccination lead to the near eradication of diseases such as tuberculosis in the developed world. Their effectiveness and easy access led to overuse, especially in live-stock raising, prompting bacteria to develop resistance. This has led to widespread problems with antimicrobial and antibiotic resistance, so much as to prompt the World Health Organization to classify antimicrobial resistance as a "serious threat [that] is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country".
The era of antibacterial chemotherapy began with the discovery of arsphenamine, first synthesized by Alfred Bertheim and Paul Ehrlich in 1907, used to treat syphilis. The first systemically active antibiotic, prontosil was discovered in 1933 by Gerhard Domagk, for which he was awarded the 1939 Nobel Prize. Sometimes the term antibiotic is used to refer to any substance used against microbes, synonymous to antimicrobial. Some sources distinguish between antibacterial and antibiotic, with antimicrobials used in soaps and cleaners etc., but not as medicine. This article treats the terms as synonymous and according to the most widespread definition of antibiotics being a substance used against bacteria.