Class C and Class D β-lactamases (AmpC and OXA β-lactamases)

Class C and Class D β-lactamases are two distinct groups of serine-based enzymes produced by bacteria to neutralize β-lactam antibiotics, representing a major mechanism of antimicrobial resistance. Class C enzymes, commonly known as AmpC β-lactamases, are typically encoded on the chromosomes of many Gram-negative bacteria or on mobile plasmids, providing resistance to penicillins and most cephalosporins (Jacoby, 2009). Class D enzymes, or OXA-type β-lactamases, are named for their ability to hydrolyze oxacillin and include variants that can degrade carbapenems, particularly in pathogens like Acinetobacter baumannii (Evans & Amyes, 2014). Both classes utilize a catalytic serine residue to initiate a nucleophilic attack on the β-lactam ring, leading to its hydrolysis and the subsequent inactivation of the drug (Bush & Bradford, 2019). These enzymes are significant therapeutic targets because they are often not inhibited by first-generation inhibitors like clavulanic acid or tazobactam. Modern clinical strategies utilize novel inhibitors such as avibactam and durlobactam, which are designed to bind these enzymes and restore the efficacy of partner antibiotics like ceftazidime or sulbactam (Livermore et al., 2018).

Other names

AmpC-type β-lactamasesOXA-type β-lactamasesSerine β-lactamasesAmbler Class CAmbler Class DOxacillinases

Inhibition of the β-lactamase enzyme through the formation of a stable, often covalent, enzyme-inhibitor complex that prevents the hydrolysis of co-administered β-lactam antibiotics (Bush & Bradford, 2019).