The accidental discovery of Penicillium notatum by Alexander Fleming lead to the production of the revolutionary drug, penicillin, a β-lactam antibiotic.

β-lactam antibiotics destroy bacterial cells by inhibiting the cross-linking between polypeptide chains in the peptidoglycan cell wall.

Penicillin mimics the D-alanyl-D-alanine residues that normally bind to the active site in the transpeptidase enzyme.

Many bacterial strains have developed resistance to penicillin by producing β-lactamase enzymes, which catalyse the hydrolysis of the antibiotic.

β-lactamase inhibitors can be used in conjunction with penicillins to allow the antibiotic to destroy the bacterial cell without being affected by the β-lactamase enzymes.