Credit for its discovery was given to Scottish scientist Alexander Fleming, though many others have previously noted anti-bacterial effects of Penicillium molds. Its discovery was considered one of the greatest breakthroughs of the 20th century in the field of medicine. However, since antibiotic resistance to early forms of penicillin and other beta-lactams is now very common, and new resistance is arising all the time, scientists are constantly working to come up with new and effective forms. Some of these have moderate to high effectiveness against Gram-negative bacteria as well.
Penicillin is grown from molds and has the general formula of C9H11N2O4SR, where "R" represents a chemical group that is different for different types of penicillin.