Survival of immunized mice challenged with wild-type Streptococcus suisstrains SS2, SS7, SS9, or SS1/2. Female BALB/c mice per group were immunized orally twice at 3-week intervals with 1 × 10 9 CFU of with attenuated Salmonella carrying either pS-SaoA, pS-Eno, pS-SE, or pYA3493 (empty vector) and PBS. Each group of mice was randomly divided into 5 subsets of ten mice each and were respectively challenged intraperitoneally with 1.2 × 108
CFU of SS2 (A), 1.0 × 108 CFU of SS7 (B), 6.3 × 108 CFU of SS9 (C), 8.5 × 108 CFU of SS1/2 (D) or PBS 2 week after boosting. The challenge dose is equal to 10 × LD50. Survival analysis was performed using the Kaplan–Meier method with the log-rank (Mantel-Cox) test. *P < 0.05; **P < 0.01; ***P < 0.001.