Ambler class A β-lactamase (Class A β-lactamase)

Ambler class A β-lactamases are serine-based enzymes produced by bacteria that hydrolyze the β-lactam ring in antibiotics such as penicillins, cephalosporins, and monobactams, conferring resistance to these drugs. They are defined by molecular homology in the Ambler classification system, which groups them separately from classes B (metallo), C, and D based on amino acid sequence and active site serine residue. Common examples include plasmid-encoded ESBLs like TEM, SHV, and CTX-M, primarily in Enterobacterales such as Escherichia coli and Klebsiella pneumoniae, as well as carbapenemases like KPC. These enzymes inactivate extended-spectrum cephalosporins and other β-lactams but are typically inhibited by compounds like clavulanate or avibactam when combined with antibiotics. In disease, they drive multidrug-resistant infections, complicating treatment of Gram-negative bacterial infections in clinical settings. Targeting them therapeutically involves β-lactam/β-lactamase inhibitor combinations to restore antibiotic susceptibility.

Other names

Extended-spectrum β-lactamases (ESBLs)Serine β-lactamases (class A)TEM β-lactamasesSHV β-lactamasesCTX-M β-lactamasesKPC (Klebsiella pneumoniae carbapenemase)

Serine-based hydrolysis of β-lactam ring. Inhibition by β-lactamase inhibitors forming stable acyl-enzyme complex.