Fig. 1

Preparation and visualization of OMVs derived from avian pathogenic Escherichia coli. a Isolation and purification protocols of bacterial OMVs. b Native OMVs were isolated and pelleted by ultracentrifugation. c OMVs were purified by Optiprep density gradient ultracentrifugation. The particle numbers of the resulting fractions (1–10) were detected by nanoparticle tracking analysis (NTA). Purified MOMV_S were visualized using scanning electron microscope (d) and transmission electron microscopy (e) after negative staining. f Representative frame was captured from the MOMVs NanoSight videos. g Size distribution and concentration of these vesicles was determined by NTA