Zinc starvation uncovers bacterial host-specific proteases that shape NDM adaptability in <i>Acinetobacter baumannii</i>

Metallo-β-lactamases, particularly New Delhi metallo-β-lactamase (NDM), threaten antibiotic therapy by disseminating across diverse bacteria. The rise of NDM-producing carbapenem-resistant <i>Acinetobacter baumannii</i> (<i>Ab</i>) highlights the risk of global spread of this pathogen. NDM-mediated resistance depends on periplasmic proteostasis, which regulates the levels of folded, metalated, and active proteins. In <i>Escherichia coli</i>, zinc limitation-common at infection sites-causes loss of the essential metal cofactors in NDM, leading to protein degradation via a specific periplasmic quality control system. Our study reveals that the mechanisms regulating NDM-1 stability under zinc starvation are highly host-dependent. Notably, we identify the proteases DegP and CtpA as responsible for NDM-1 degradation in <i>Ab</i>, differing from the process in <i>E. coli</i>. In-cell stability of NDM in <i>Ab</i> is highly variable depending on minor mutations in CtpA from clinical strains, as well as by mutations in the allelic variants of this β-lactamase. Particularly, NDM-5 displays a higher stability and confers an enhanced resistance phenotype that may help <i>Ab</i> thrive under zinc-limiting conditions. These results reveal selective pressures driving NDM adaptation to each bacterial host. Understanding how pathogens engage their periplasmic metabolism to regulate NDM levels offers insights into the overlooked role of host-specific adaptation of resistance mechanisms. These findings highlight the importance of developing host-directed therapeutic interventions based on the understanding of protein cell homeostasis. In this regard, exploiting host-specific proteases as targeted tools to destabilize resistance enzymes represents a novel therapeutic avenue for curbing the spread of NDM in different pathogens.IMPORTANCEThe alarming rise of <i>Acinetobacter baumannii</i> producing New Delhi Metallo-β-lactamase (NDM) threatens last-line antibiotic therapies. While β-lactamase dissemination is often accounted for the underlying genetics, the biochemical mechanisms involved in the adaptation of these enzymes within specific bacterial hosts are scarcely known. Here, we show that the stability of NDM differs significantly between <i>A. baumannii</i> and <i>Escherichia coli</i>, due to the varying roles of periplasmic proteases involved in NDM degradation in each host. Variant NDM-5 exhibits enhanced stability and confers increased antibiotic resistance in <i>A. baumannii</i> under zinc-limited conditions (common in infection sites). These findings underscore the role of host-specific proteostasis in shaping the adaptation of resistance determinants and suggest new strategies to combat antibiotic resistance.