Fig 2. S19-GFP displays similar biological properties to the parental S19 strain and requires constitutive GFP expression for sustaining anti-GFP antibody levels in mice.

(A) In vitro growth kinetics in TSB medium of B. abortus S19 and S19-GFP strains. (B) Replication kinetics of B. abortus S19-GFP, S19, and 2308-GFP strains in HeLa cells. (C) Groups of 25 mice were inoculated intraperitoneally with 1×10⁶ CFU of B. abortus S19-GFP or S19, and the mean ± SD (n = 5) of log₁₀CFU/spleen were assessed at selected intervals. (D) Groups of 5 mice were intraperitoneally inoculated either with a mixture of 1×10⁵ CFU of S19 + 20 μg of GST-GFP or with a mixture 1×10⁵ CFU of S19-GFP + 20 μg of GST-GFP and the level of anti-GFP antibodies in serum (expressed as log₂ OD) assessed by ELISA-GFP at the indicated times after inoculation. * Fisher´s PLSD test: p ≤ 0.05.