Penicillin is an antibiotic that is used to treat bacterial infections. Penicillin kills susceptible bacteria by specifically inhibiting the transpeptidase that catalyzes the final step in cell wall biosynthesis, the cross-linking of peptidoglycan. Penicillin was first identified by Alexander Fleming when he accidentally left the lid of one of his petri dishes open and returned to find the Penicillin notatum fungi developing on the dish generating Penicillin. .
M.Lobanovska and G.Pilla. Penicillin's discovery and Antibiotic resistance: Lessons for the future? Yale J biol Med. 2017, 90(1):135-145