Most antibiotics Greek anti,"against;"bios,"life" are substances produced by microbes that are used to kill or stop the growth of other microbes except viruses. Around 90% of antibiotics are natural substances produced by bacteria. Other antibiotics come from fungi and a few are synthetic compounds created in a laboratory.

Antibiotics represent our first great victory in treating disease. And they were discovered by accident. In 1928, a Scottish scientist named Alexander Fleming working in London returned from vacation to discover that one of his laboratory dishes containing bacteria was overgrown with mold. Fleming had been studying the bacteria and now thought his experiment was ruined. But instead of simply throwing it away, he made the now historic decision of examining it. He found that the mold was secreting yellow droplets of liquid that killed the bacteria.

In later experiments he discovered that his mold juice killed the bacteria that caused pneumonia, scarlet fever, meningitis, diphtheria and other dangerous diseases. Fleming had discovered the first antibiotic, penicillin. Penicillin, and the antibiotics that followed have become known as wonder drugs. For the first time, it became possible to cure deadly bacterial diseases that had plagued humans throughout history. Antibiotics have changed our lives.