Table 4.

Oral immunization with PspA-expressingSalmonella strains protects BALB/cJ mice against i.p. challenge with 3 × 103 CFU of capsular type 3 S. pneumoniae

Vaccine strainaPspA expressionbNo. of mice% Alive on post- challenge daycMedian day of deathd
215
χ4550(pYA3193)+359766>15.0**
χ4550(pYA3148)10100304.0
None (not immunized)NA108003.0*
  • a Mice were orally immunized two times at 1-month intervals with the indicated vaccine strains.

  • b +, PspA expressed; −, PspA not expressed; NA, not applicable.

  • c Four weeks after the second oral immunization, mice were challenged in two experiments with approximately 3 × 103 CFU of S. pneumoniae WU2. Both experiments gave similar results, and the data from each have been pooled for presentation and analysis. The LD50 of WU2 in nonimmunized BALB/c mice was <102 (data not shown).

  • d * and **, respectively, indicate Pvalues of 0.009 and 0.004 versus the time to death of mice immunized with the PspA vector pYA3148, as calculated by the two-tailed Wilcoxon two-sample rank test.