FIGURE 4.

Competitive index of the ΔSaeRS mutant vs. total bacterial count. In vivo, the brain, spleen, and liver of tilapia (Oreochromis niloticus) infected with the mixed inoculum of the S. agalactiae THN0901 and ΔSaeRS strains were sampled and counted after 3, 6, and 12 h, respectively (A). In vitro, the mixture of S. agalactiae THN0901 and ΔSaeRS stains was inoculated in a fresh brain heart infusion (BHI) medium, and the bacterial liquid was sampled and counted after 2, 4, 6, 9, 12, and 24 h, respectively. Samples were tested in triplicate. A competitive index of 0.5 indicated that the ΔSaeRS mutant strain with THN0901 strain was proliferating equally (B). Each experiment was performed in triplicate, and data were presented as mean ± standard deviation (SD), *: 0.01 < P < 0.05, **: P < 0.01.