TABLE 3.

Mortality rates of DBA2 neonate mice challenged with the ETEC 258909 strain, which had been incubated with serum pools from mice subjected to different immunization regimens

Serum samplea	Anti-CfaB titerb	No. of deaths/no. of inoculated mice (%)c
Nonimmunized		8/8 (100)
pRECFA	4,268	12/12 (100)
pRE4 + HG3	420	10/10 (100)
pRECFA + HG3 4w	10,663	2/11 (18)*
CFA/I fimbriae	14,753	2/8 (25)*

^aTested serum samples were as follows: nonimmunized mice; pRECFA, mice immunized with two i.m. pRECFA doses; HG3, mice vaccinated with two p.o. doses of the HG3 strain; pRE4 + HG3, mice immunized with two doses of pRE4 followed 2 weeks later by two booster doses with the HG3 strain; pRECFA + HG3 4w, mice subjected to the primer-booster regimen, with a 4-week interval between the last DNA dose and the first Salmonella booster; CFA/I, mice vaccinated with three i.p. doses (10 μg each) of purified CFA/I fimbriae.

^bTiters of the tested serum samples, as determined for IgG ELISA plates coated with denatured CFA/I fimbriae.

^cMortality rates of DBA2 neonate mice after challenge with 2 × 10⁷ CFU of the ETEC 258909 strain, which was previously incubated for 1 h with the tested serum samples. Serum samples were tested at a final dilution of 1:25 (HG3, nonimmune, and pRECFA + HG3 4w) or 1:50 (CFA/I). *, statistically different value (P < 0.05) compared with the results obtained with serum samples from mice immunized with pRECFA.