TABLE 2.

Oral immunization with PspA-expressing Salmonella strains protects BALB/c mice against intraperitoneal challenge with capsular type 3 S. pneumoniae WU2

Vaccine strainaPromoterPresence of lacI/pspAbNo. of challenged miceNo. of days to death (no. of mice)c% survivald
χ9241(pYA4088)Ptrc+/+223 (4), 4 (8), >15 (10)45.5e
χ9555(pYA4571)PssaG−/+232 (2), 3 (8), 4 (3), 5 (1), >15 (9)39.1f
χ9555(pYA4572)PpagC−/+223 (7), 4 (7), >15 (8)36.4g
χ9241(pYA4571)PssaG+/+202 (4), 3 (11), 4 (1), 5 (1), >15 (3)15
χ9241(pYA4572)PpagC+/+202 (2), 3 (6), 4 (2), 5 (1), >15 (9)45h
χ9241(pYA3493)Ptrc+/−82 (5), 3 (3)0
χ9555(pYA4569)PssaG−/−82 (5), 3 (3)0
χ9555(pYA4570)PpagC−/−82 (4), 3 (4)0
χ9241(pYA4569)PssaG+/−32 (2), 3 (1)0
χ9241(pYA4570)PpagC+/−33 (3)0
  • a Mice were orally immunized with two doses of the indicated vaccine strains at 0 and 6 weeks.

  • b +, presence; −, absence.

  • c Ten weeks after the primary oral immunization, mice were challenged with approximately 2 × 104 CFU of S. pneumoniae WU2. The LD50 of WU2 in nonimmunized BALB/c mice is 2 × 102 CFU (53).

  • d The survival data were analyzed using the Kaplan-Meier method, and survival comparisons were done by the Mantel-Cox test method.

  • e Compared to χ9241(pYA4571)-immunized mice, P = 0.002. Compared to χ9241(pYA3493)-immunized mice, P < 0.001.

  • f Compared to χ9241(pYA4571)-immunized mice, P = 0.046. Compared to χ9555(pYA4569)-immunized mice, P < 0.001.

  • g Compared to χ9555(pYA4570)-immunized mice, P < 0.001.

  • h Compared to χ9241(pYA4571)-immunized mice, P = 0.03.