BackgroundMesenchymal stem cell (MSC) derived extracellular vesicles (EVs) have been proposed as an alternative to cell therapy, creating new possible delivery modalities such as nebulisation. We wished to investigate the therapeutic potential of directly nebulised MSC-EVs in the mitigation ofEscherichiacoli-induced pneumonia.MethodsEV size, surface markers and miRNA content were assessed pre- and post-nebulisation. BEAS2B and A459 lung cells were exposed to lipopolysaccharide (LPS) and treated with nebulised bone marrow (BM) or umbilical cord (UC) MSC-EVs. Viability assays (MTT) and inflammatory cytokine assays were performed. THP-1 monocytes were stimulated with LPS and nebulised BM- or UC-EVs and phagocytosis activity was measured. For in vivo experiments, mice received LPS intratracheally (IT) followed by BM- or UC-EVs intravenously (IV) and injury markers assessed at 24 h. Rats were instilled withE. colibacteria IT and BM- or UC-EVs delivered IV or by direct nebulisation. At 48 h, lung damage was assessed by physiological parameters, histology and inflammatory marker presence.ResultsMSC-EVs retained their immunomodulatory and wound healing capacity after nebulisation in vitro. EV integrity and content were also preserved. Therapy with IV or nebulised MSC-EVs reduced the severity of LPS-induced lung injury andE. coli-induced pneumonia by reducing bacterial load and oedema, increasing blood oxygenation and improving lung histological scores. MSC-EV treated animals also showed lower levels of inflammatory cytokines and inflammatory-related markers.ConclusionsMSC-EVs given IV attenuated LPS-induced lung injury, and nebulisation of MSC-EVs did not affect their capacity to attenuate lung injury caused byE. colipneumonia, as evidenced by reduction in bacterial load and improved lung physiology.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13287-023-03385-6.