Antigen-Displaying Outer Membrane Vesicles from Engineered Probiotics for Combating

The clinical use of broad-spectrum antibiotics often disrupts the host microbiota, increasing the risk and severity of Pseudomonas aeruginosa infections. To address this, we developed a novel probiotic-based immunization strategy using an antibiotic-induced susceptible mouse model. Specifically, we first selected the probiotic Escherichia coli Nissle 1917 (EcN) —the only non-pathogenic E. coli strain with well-documented biosafety and the ability to enhance host immune function to produce outer membrane vesicles (OMVs) displaying either the OprI or PpyR antigen from P. aeruginosa, which possess inherent immunostimulatory activity suitable for vaccine development and self-assembling surface display capability. Upon comparing these OMVs through intranasal immunization, OMVs displaying OprI, an antigen that elicits a robust mucosal immune response associated with Th17 cell polarization, demonstrated superior protective efficacy. Building on this result, we then constructed an orally engineered probiotic strain, EcN- OMV-OprI, designed for gut colonization and the sustained secretion of antigen-displaying OMVs. In antibiotic-pretreated mice, the oral administration of EcN-OMV-OprI significantly increased the 7-day survival rate from 0% to 80% following P. aeruginosa infection and effectively suppressed bacterial burden in the lungs. Together, these findings present a safe and promising strategy for preventing secondary P. aeruginosa infections following clinical antibiotic exposure.