Beyond Catalysis: Physiology, Cellular Biology And Therapeutic Strategies for Metallo-β-Lactamase-Producing Pathogens

Abstract Metallo-β-lactamases (MBLs) are zinc-dependent β-lactamases that threaten the clinical utility of carbapenems and other last-line β-lactams in Gram-negative pathogens. Their impact cannot be explained solely based on their catalytic efficiency. Clinically relevant MBLs differ in substrate profiles, cellular localization, metal dependence, periplasmic stability, and host compatibility. These features shape both resistance phenotypes and the dissemination of MBL genes after horizontal transfer. Recent therapeutic progress has exploited vulnerabilities in this landscape. Cefiderocol circumvents permeability barriers through siderophore-mediated uptake but can be compromised by expression of New Delhi MBL and iron-transport defects. Aztreonam, uniquely stable to most B1 MBLs, has been revived through protection by avibactam against coproduced serine β-lactamases. Zidebactam-containing combinations exploit β-lactam enhancement targeting penicillin-binding protein 2 rather than direct MBL inhibition. Meanwhile, broad-spectrum boronates such as taniborbactam and xeruborbactam illustrate both the promise and the evolutionary fragility of direct inhibitor strategies. Beyond therapeutics, emerging work on MBL biogenesis, zinc limitation, periplasmic protein quality control, and host-specific expression reveals that resistance is a physiological phenotype, not simply an enzymatic trait. This review integrates biochemical, cellular, evolutionary, and clinical perspectives to highlight why MBL-mediated resistance requires context-aware diagnostics, surveillance, and precision therapeutic decisions.