Antibiotics or antibacterials are a type of antimicrobial used in the treatment and prevention of bacterial infection.They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity.Antibiotics are not effective against viruses such as the common cold or influenza, and may be harmful when taken inappropriately. In 1928, Alexander Fleming identified penicillin, the first chemical compound with antibiotic properties. Fleming was working on a culture of disease-causing bacteria when he noticed the spores of little green mold in one of his culture plates. He observed that the presence of the mold killed or prevented the growth of the bacteria.
Sometimes the term antibiotic is used to refer to any substance used against microbes, synonymous to antimicrobial, leading to the widespread but incorrect belief that antibiotics can be used against viruses. Some sources distinguish between antibacterial and antibiotic; antibacterials used in soaps and cleaners etc., but not as medicine