Fig. 1

a Electron micrograph of ETEC O101:K99—derived OMVs. To confirm final product purification of ETEC culture supernatant and vesicles morphology, they were negatively stained and visualize by Transmission electron microscopy. Image was obtained by ZEISS EM900. Bar = 100 nm. Survival rates of respective offspring from immunized and sham-immunized mice. To evaluated the effect of OMV-and sham (PBS) immunization regime on neonatal mice protect against ETEC, b suckling offspring (n = 50–53, each group) after 24 h of birth challenged orally with lethal doses of ETEC (10³ CFU) and survival was monitored every 12 h for 7 days. c suckling offspring (n = 50–53, each group) after 24 h of birth challenged orally with lethal doses of ETEC (10² CFU) and survival was monitored every 12 h for 7 days d Likewise, respective suckling offspring (n = 52–63, each group) from OMVs plus avD3-and sham (PBS + avD3) immunization mice, after 24 h of birth challenged orally with 10³ CFU. All sham-immunized mice died in the first 24 and 48 h after challenged with 10³ and 10² CFU of bacteria respectively. e Survival rate comparison between OMV-immunized group and OMV plus avD3-immunized group. No significant difference was observed in survival rate due to use avD3. f Ascites was seen as post mortem symptom in all neonatal mice that had no ability to resist against disease (black arrow)