Outer membrane vesicles transmit blaNDM-5 and package metallo-β-lactamases to promote antibiotic resistance in Escherichia coli.

OBJECTIVES

Outer membrane vesicles (OMVs) are nanoscale proteoliposomes secreted by Gram-negative bacteria that have emerged as important mediators of antibiotic resistance dissemination. This study aimed to elucidate the structural, functional and proteomic characteristics of OMVs derived from Escherichia coli carrying the blaNDM-5 gene and to determine their contribution to carbapenem resistance transfer and bacterial adaptation.

METHODS

OMVs were isolated from E. coli strains with or without blaNDM-5 expression and characterized by transmission electron microscopy, dynamic light scattering and zeta potential analysis. The presence of blaNDM-5 and β-lactamase activity in OMVs was confirmed by PCR and ELISA. Horizontal gene transfer was evaluated using a bioluminescent E. coli recipient strain under selective pressure. LC-MS/MS proteomics was performed to assess changes in OMV protein composition associated with blaNDM-5 expression.

RESULTS

OMVs from blaNDM-5-positive E. coli encapsulated both blaNDM-5-bearing plasmids and catalytically active NDM-5 carbapenemase, enabling horizontal transfer of functional resistance to susceptible recipients. Acquisition of OMV-delivered plasmids increased meropenem MICs by over 500-fold, while OMV-associated β-lactamase activity reduced antibiotic efficacy in the extracellular environment and protected nearby susceptible bacteria. Proteomic profiling further revealed that blaNDM-5 expression was accompanied by broad changes in OMV protein composition, consistent with global cellular adaptations to carbapenem exposure.

CONCLUSIONS

bla NDM-5-positive OMVs promote carbapenem resistance through dual mechanisms involving plasmid-mediated gene transfer and extracellular antibiotic degradation. These findings extend prior work on OMV-associated carbapenemase activity and identify bacterial vesicles as an underappreciated but potentially important contributor to the dissemination and maintenance of carbapenem resistance.