Proliferation and significance of clinically relevant β-lactamases

Inactivation of β-lactam antibiotics by β-lactamases in bacterial infections is associated with some of the most serious infectious disease issues that are currently encountered. The evolution of unique β-lactamases has resulted in more than 1,300 distinct enzymes that have been identified in natural clinical isolates. Of these enzymes, the most deleterious β-lactamases are the extended-spectrum β-lactamases, or ESBLs, that hydrolyze most penicillins and cephalosporins, and the carbapenemases that may inactivate all β-lactam classes of drugs. The most prominent ESBLs worldwide are the CTX-M-14 and CTX-M-15 enzymes. Among enzyme families, the TEM and OXA β-lactamases exhibit the greatest number of variants. The broad groups of carbapenemases are particularly treacherous, especially the KPC serine carbapenemases and the NDM family of metallo-β-lactamases, both of which appear in multidrug-resistant Gram-negative pathogens that are often resistant to most classes of antibiotics. Although new β-lactamase inhibitor combinations are being investigated as a means of controlling infections caused by these organisms, additional approaches are sorely needed.