Fig. 8
The evaluation of protection induced by the physical mixtures of three different OMVs against infection with multiple E. coli strains. These three OMVs, which display E. coli O26 and O111, and O145 and O103 in addition to O111 and O157, respectively, were physically mixed in PBS and administered intraperitoneally to six groups of female mice on days 0 and 14 with a dose containing 1 µg of each OMV in 100 µl PBS. The immunized mice underwent an intraperitoneal challenge with wild-type E. coli O26 (A), O45 (D), O111 (B), O157 (E), O145 (C), and O103 (F) were 8 × 108 CFU/100 µl, 1.5 × 108 CFU/100 µl, 5 × 107 CFU/100 µl, 5.3 × 106 CFU/100 µl, 6.5 × 107 CFU/100 µl, and 3.8 × 108 CFU/100 µl, respectively, at week 8 after the initial immunization. Following the challenge, mortality was recorded for 12 days. Data from six independent experiments were summarized (n = 8). Mouse survival differences were analyzed using the log-rank test, with the Kaplan-Meier survival curve used for monitoring; superscript letters a and b indicate P < 0.05 for comparisons with the PBS and OMV vector groups, respectively