In 1928, bacteriologist Alexander Fleming was studying Staphylococcus, a type of bacteria that can cause serious infections. He grew the bacteria in small containers called
petri dishes. One day he noticed that mold had accidentally been introduced into one of
the petri dishes and was startled to see that there were no bacteria around the moldy
area. Fleming correctly deduced that the mold had had an antibacterial effect; somehow
it had prevented the bacteria from growing. Fleming identified the mold as the strain
Penicillium notatum and called its antibacterial ingredient-which he was unable to
successfully extract-penicillin. Fleming's discovery of penicillin's unique effect led to the
eventual finding that it could be used to treat infections. Several years after his initial
observation, scientists built on his work by extracting penicillin from mold and
demonstrating its effectiveness as a treatment.