TABLE 2.

Oral immunization with rPspA-expressing S. enterica serovar Typhimurium χ8501(pYA3494) vaccine protects BALB/c mice against challenge with virulent S. pneumoniae strain WU2

VaccinearPspA expressionbProtectionc (% alive)Days to death
5, 5
χ8501(pYA3494)+60*
>21, >21, >21
χ8501(pYA3493)01, 2, 2, 3, 3
None (unimmunized)NA01, 2, 2, 2, 3
  • a Mice were orally immunized a total of two times at 10-week intervals with ∼109 CFU of indicated vaccine strain per dose.

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

  • c Five weeks after the last immunization, mice (five mice per group) were challenged intraperitoneally with approximately 4.8 × 103 CFU of virulent S. pneumoniae WU2. The LD50 of WU2 by intraperitoneal infection in unimmunized BALB/c mice was <102 (data not shown). Mortality was monitored for 3 weeks after pneumococcal challenge. Significance was determined by chi-square analysis. ∗, P < 0.05.