Membrane anchoring of New Delhi metallo‐β‐lactamase‐1 alters the fitness of Escherichia coli and increases its susceptibility to colistin by inducing outer membrane destabilization

New Delhi metallo‐β‐lactamase‐1 (NDM‐1)‐producing bacteria are resistant to nearly all available β‐lactam antibiotics and have become a public health threat. Antibiotic resistance often carries fitness costs, which typically manifest as a reduced bacterial growth rate. Here, we investigated the mechanism of fitness cost in NDM‐1‐producing bacteria. Our findings revealed that strains expressing bla NDM‐1 exhibited a significant growth defect under high osmotic stress. This fitness cost was attributed to the anchoring of NDM‐1 to the bacterial outer membrane via its leader peptide, which destabilized the outer membrane. Replacing the membrane‐anchoring residue Cys26 in the leader peptide with alanine not only restored outer membrane stability but also ameliorated the bacterial fitness cost. Furthermore, the anchoring of NDM‐1 to the membrane increased bacterial susceptibility to the membrane‐disrupting antibiotic colistin, both in vitro and in vivo , as confirmed in engineered and clinically isolated strains. In conclusion, membrane anchoring of NDM‐1 increased the permeability of the bacterial outer membrane, thereby reducing the fitness of NDM‐1‐producing bacteria and enhancing their susceptibility to colistin. These results not only elucidate the mechanism of fitness cost associated with NDM‐1 but also provide new insights into the rational use of colistin to combat infections caused by NDM‐1‐producing bacteria.