Figure 7.
Sf2a-specific serum bactericidal assays (A) and protection of mice against the challenge of virulent Sf2a strain 2457T (B). (A) Serially diluted serum from each group collected on Day 28 (two weeks after secondary immunization) were used to determine and assay the percentages of killed 2457T. (B) Female BALB/c mice immunized with 2 doses of vaccine strains (1 × 109 CFU per dose) expressing Sf2a O-antigen showed significantly greater protection against the challenge of 2457T (5 × 107 CFU per mouse) through the intraperitoneal route two weeks after the secondary immunization, compared to the empty-plasmid and BSG controls. * P < 0.05 compared to BSG, ** P<0.01 compared to BSG, *** P <0.001 compared to BSG, # P < 0.05 compared to Vac5, ## P <0.01 compared to Vac5, ### P <0.001 compared to Vac5.