A Review on Extended Spectrum β-Lactamase and Metallo β-Lactamase Producing Bacteria: From Current Understanding to Future Course of Action

The growing prevalence of multidrug-resistant Gram-negative bacteria, particularly those producing extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs), presents a serious global health threat. These enzymes degrade a wide range of β-lactam antibiotics, undermining treatment efficacy. ESBLs (e.g., CTX-M, TEM, SHV) mainly target third-generation cephalosporins and are commonly found in Escherichia coli and Klebsiella pneumoniae. MBLs (e.g., NDM, VIM, IMP) confer broader resistance, including to carbapenems, and are not inhibited by β-lactamase inhibitors. Rapid gene transfer via mobile elements accelerates their spread in hospitals and communities.

This review outlines the molecular classification, resistance mechanisms, detection methods, and clinical impact of ESBL and MBL producers. It highlights current diagnostic challenges—especially for MBLs—and reviews phenotypic and molecular tools. Treatment options are increasingly limited, with carbapenems reserved for ESBL infections and few effective agents for MBLs. Co-existence of ESBL and MBL genes in single strains further complicates therapy and infection control. Mitigating this threat demands global surveillance, rapid diagnostics, prudent antibiotic use, and the development of novel drugs or inhibitors. A deeper understanding of resistance dynamics is essential to inform research, clinical practice, and policy.