Fig. 6

Immunization with MOMVs conferred cross-protection against infection of three APEC serogroups. a Survival rates of MOMVs- and PBS-immunized chickens after challenges of these three APEC serogroups (O1, O2 and O78). Chickens were immunized intramuscularly with MOMVs (10, 50 and 100 μg) or PBS at weekly intervals for 3 weeks (day 7, day 14 and day 21) (n = 20), and then challenged by the intratracheal route with the lethal dose (LD) of each APEC serogroup after the last immunization, respectively. b Survival rates of MOMVs (50 μg)- and PBS-immunized birds challenged with each APEC serogroup (2× LD) 5 weeks (day 56) after the last immunization (n = 10). The difference between each group was analyzed using the Kaplan–Meier method. Survival rate of each group was calculated every day for 10 days. **P < 0.01; ***P < 0.001; versus the control (PBS)