Class A serine β-lactamase enzyme (Class A β-lactamase)

Class A serine β-lactamase enzymes are bacterial enzymes that confer resistance to β-lactam antibiotics—including penicillins, cephalosporins, and, in some variants, carbapenems—by catalyzing the hydrolysis of the β-lactam ring, which deactivates the antibiotic molecule. They function via a conserved serine residue (Ser70) in their active site, which participates in a two-step mechanism: acylation (covalent bonding of antibiotic to the enzyme) followed by deacylation (release of the hydrolyzed, inactive product). These enzymes are evolvable, with numerous variants (TEM, CTX-M, KPC, SHV) that differ in substrate specificity and inhibitor sensitivity. Their expression is a key driver of multi-drug-resistant infections, especially in Gram-negative bacterial pathogens. Monitoring their presence and activity is important for infection control, antibiotic stewardship, and treatment decisions.

Other names

Class A β-lactamaseSerine β-lactamase (Class A)Penicillinase (for many Class A types)TEM-type β-lactamaseCTX-M-type β-lactamaseKPC-type β-lactamaseSHV-type β-lactamase

Substrate hydrolysis: The enzyme hydrolyzes the four-membered β-lactam ring in β-lactam antibiotics, inactivating them Enzyme inhibition: β-lactamase inhibitors covalently bind to active-site serine or block the enzyme, preventing antibiotic degradation Competitive inhibition: Some drugs competitively bind to enzyme active sites but are not hydrolyzed