Class A CTX-M beta-lactamase (CTX-M)

Class A CTX-M beta-lactamases are a critical group of enzymes that confer high-level resistance to third-generation cephalosporins, particularly cefotaxime (Bonnet, 2004). Originally identified in the late 1980s, these enzymes have rapidly spread globally and are now the most common extended-spectrum beta-lactamases (ESBLs) found in clinical isolates of Enterobacteriaceae, such as Escherichia coli (D'Andrea et al., 2013). They function by using a catalytic serine residue to hydrolyze the beta-lactam ring of antibiotics, thereby inactivating them before they can reach their bacterial targets (Livermore, 2008). The genes encoding these enzymes, such as blaCTX-M-15, are frequently located on mobile plasmids, facilitating their rapid dissemination across different bacterial species. Clinically, CTX-M-producing organisms are associated with increased morbidity and mortality due to limited treatment options. Therapeutic management often relies on combining beta-lactam antibiotics with modern inhibitors like avibactam or vaborbactam, which are designed to overcome the hydrolytic activity of these enzymes and restore antibiotic susceptibility (Bush & Bradford, 2016).

Other names

CefotaximaseCTX-M-type beta-lactamaseExtended-spectrum beta-lactamaseESBLAmbler Class A beta-lactamase

Beta-lactamase inhibitors act by binding to the active-site serine of the CTX-M enzyme, forming a stable acyl-enzyme intermediate that prevents the enzyme from degrading beta-lactam antibiotics (Bush & Bradford, 2016).