Penicillin, the first antibiotic, was discovered in 1928 by Alexander Fleming in London, England. Fleming made his discovery when he noticed that bacteria could not survive on a culture plate that contained a mold commonly found on bread.
Scientists spent the next few years learning to purify the penicillin from the mold. By the early 1940s, penicillin was widely available. Not long after, other antibiotics were discovered.
The discovery of penicillin was considered a medical miracle because it helped wipe out many of the diseases that are caused by bacteria. This meant that deadly diseases such as tuberculosis, pneumonia, syphilis and tetanus could now be treated. With time, however, bacteria started to become resistant to antibiotics or not affected at all.