Table 2. Protective efficacy of S19-GFP and S19 strains against virulent B. abortus in mice^a.

Group	Log10 B. abortus 2308 CFU /spleen (mean ± SD)	Protection Units
S19-GFP	1.94 ± 1.08 b	4.36
S19	2.52 ± 1.03 b	3.78
Unvaccinated	6.30 ± 0.23	--

^a Groups of CD-1 mice (n = 5) were vaccinated subcutaneously with 1x10⁵ B. abortus S19-GFP CFU or 1x10⁵ B. abortus S19 CFU. The unvaccinated controls were injected subcutaneously with 0.1 mL of sterile PBS. Four weeks after that, all mice were challenged intraperitoneally with 5x10⁴ CFU of virulent B. abortus 2308 strain. Two weeks later, the number of viable bacteria in the spleen was determined. The efficacy of vaccination was expressed as the mean ± SD (n = 5) of individual log₁₀ CFU/spleen of B. abortus 2308 challenge strain.

^b p < 0.001 vs. unvaccinated controls. No significant differences were obtained between S19 and S19-GFP vaccines.