. 1998 Aug;66(8):3744–3751. doi: 10.1128/iai.66.8.3744-3751.1998

TABLE 4.

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

Vaccine strain^a	PspA expression^b	No. of mice	% Alive on post- challenge day^c		Median day of death^d
Vaccine strain^a	PspA expression^b	No. of mice	2	15	Median day of death^d
χ4550(pYA3193)	+	35	97	66	>15.0**
χ4550(pYA3148)	−	10	100	30	4.0
None (not immunized)	NA	10	80	0	3.0*

Mice were orally immunized two times at 1-month intervals with the indicated vaccine strains.

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

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).

* and **, respectively, indicate P values 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.