May 10th 1929 is a very important day in drug discovery research, it was on this day that Alexander Fleming submitted his paper entitled "On the Antibacterial Action of Cultures of a Penicillium, with Special Reference to their Use in the Isolation of B. influenzæ" Br J Exp Pathol. 1929 Jun; 10(3): 226–236.

Over 90 years later this chance discovery still has a major impact on health today. Whilst isolation proved too challenging for Fleming he sent his Penicillium mold to anyone who requested it in hopes that they might isolate penicillin. It was only in 1940 that Howard Florey and team published the isolation and purification of Penicillin. Penicillin as a chemotherapeutic agent. Lancet. 1940;236:226–8. 10.1016/S0140-6736(01)08728-1.

The basic structure of the beta-lactam ring is shown below.

The beta lactam antibiotics (Penicillin and Cephalosporins) are a very well studied class of therapeutic agent, the mechanism of action is the inhibition of cell wall synthesis. Penicillin inhibits the formation of peptidoglycan cross-links in the bacterial cell wall; this is achieved through reaction of the β-lactam ring of penicillin to the enzyme DD-transpeptidase. As a consequence, DD-transpeptidase cannot catalyze formation of the cell wall cross-links.