Class A beta-lactamase enzyme; Class C beta-lactamase enzyme (None standard; commonly used abbreviations include TEM, SHV, CTX-M for Class A, and AmpC for Class C, but these refer to specific enzyme families or types rather than the whole class[5][7][8].)

Class A and class C beta-lactamase enzymes are serine-active enzymes produced by bacteria that confer resistance to beta-lactam antibiotics (such as penicillins and cephalosporins) by hydrolyzing the amide bond of the beta-lactam ring[1][8]. Class A beta-lactamases include many major broad-spectrum enzymes (such as TEM, SHV, CTX-M), using a conserved serine in the active site, and are often plasmid-encoded, facilitating horizontal gene transfer[3][4][6]. Class C beta-lactamases (cephalosporinases or AmpC enzymes) are typically chromosomally encoded and confer resistance primarily to cephalosporins, but also to penicillins, and are notable for their resistance to many beta-lactamase inhibitors[5][9]. Both play major roles in clinical antibiotic resistance and are key drug targets for the development of new beta-lactamase inhibitors[4][5][8]. **Note:** For structured data purposes, Class A beta-lactamase enzyme and Class C beta-lactamase enzyme **should be listed separately** due to clear biochemical, phylogenetic, and clinical distinctions[1][5][6][9].

Other names

Beta-lactamase Class ABeta-lactamase Class CSerine beta-lactamase (applies to both A and C, as both use a serine in the active site)Cephalosporinase (commonly for Class C/AmpC)Extended-spectrum beta-lactamase (may apply to certain class A)AmpC beta-lactamase (Class C)TEM, SHV, CTX-M (examples from Class A)Various enzyme family names: ACT, ACC, ADC, CMH, CMY, FOX, MOX, PDC, TRU (mostly Class C)[5][9]

Hydrolysis of the beta-lactam ring in antibiotics, rendering them inactive[8] Acyl-enzyme intermediate (serine acts as nucleophile in both classes) Resistance mechanism against beta-lactam drugs