Nanoparticle reinforced bacterial outer-membrane vesicles effectively prevent fatal infection of carbapenem-resistant Klebsiella pneumoniae.

Infection resulting from carbapenem-resistant Klebsiella pneumoniae (CRKP) is an intractable clinical problem. Outer membrane vesicles (OMVs) from CRKP are believed to be potential vaccine candidates. However, their immune response remains elusive due to low structural stability and poor size homogeneity. In this study, hollow OMVs were reinforced internally by size-controlled BSA nanoparticles to obtain uniform and stable vaccines through hydrophobic interaction. The result showed that the BSA-OMV nanoparticles (BN-OMVs) were homogenous with a size around 100 nm and exhibited a core-shell structure. Remarkably, subcutaneous BN-OMVs vaccination mediated significantly higher CRKP specific antibody titers. The survival rate of the mice infected with a lethal dose of CRKP was increased significantly after BN-OMV immunization. The adoptive transfer experiment demonstrated that the protective effect of BN-OMVs was dependent on humoral and cellular immunity. This study demonstrated that the structure optimization improved the immune efficacy of OMVs for vaccine development against CRKP.