FIG. 6.
Oral immunization with PspA-expressing Salmonella strains protects BALB/c mice against i.p. challenge with S. pneumoniae WU2. Nine (control) or 11 to 13 (vaccine) mice per group were orally immunized twice at 4-week intervals with the indicated vaccine strains. The mice were challenged with 4 × 104 CFU of S. pneumoniae WU2 (200 LD50) 4 weeks after the second oral immunization. Mortality was monitored for 3 weeks after pneumococcal challenge. The numbers in parentheses refer to the number of surviving mice and the total number of mice per group. All vaccine groups were significantly different from the χ9241(pYA3493) (RfaH+) control (P < 0.01). χ9884(pYA4088) (ΔrfaH49) versus χ9852(pYA4088) (ΔPrfaH178), P = 0.0326.