Bacterial Resistance to Penicillins

β-Lactamases and Resistance to Penicillins

• Bacterial β-lactamases or penicillinase enzymes can hydrolyze the β-lactam ring, making penicillins ineffective.
• There are four classes of β-lactamases, which can recognize and hydrolyze various β-lactam molecules.
• TEM-1, a β-lactamase, recognizes mainly penicillins, but a single amino acid mutation can cause it to prefer cephalosporins.
• New β-lactamases have been discovered that can hydrolyze directly-modified β-lactams.

Discovery of β-Lactam Antibiotics

• Cephalosporin C, discovered in the 1950s, is a potent inhibitor of the enzyme in penicillin-resistant Staphylococcus aureus.
• Penicillin G, or benzylpenicillin, was isolated by Florey and Chain, leading to the development of new β-lactams.
• β-Lactam antibiotics are based on a bicyclic ring called β-lactam, which comprises the core chemical structure of penicillins.
• The β-lactam nucleus is essential for biological activity, forming a single reactive center of the molecule.

Importance of β-Lactam Antibiotics

• The discovery of penicillin by Alexander Fleming in 1928 led to extensive chemical modification of its natural structure, resulting in semi-synthetic β-lactams.
• β-Lactam antibiotics are a class of natural and synthetic antibiotics with potent antimicrobial activity due to their structural similarities to the D-alanyl-D-alanine terminus of the peptidoglycan stem pentapeptide.
• β-Lactam antibiotics function by inhibiting the function of penicillin-binding proteins, which catalyze the formation of peptidoglycan crosslinks.