FIG 5.

Intracellular growth of S. agalactiae in RAW264.7 macrophages. (A) Intracellular survival of wild-type S. agalactiae GD201008-001 in RAW264.7 macrophages compared to that of the ΔhylB mutant and complemented strains infected at an MOI of 1. Phagocytosis was allowed to proceed for 1 h before the addition of antibiotics for 1 h. This initial antibiotic treatment was extended for different times up to 24 h. The relative number of CFU (rCFU) was estimated by plating out the lysates of infected macrophages and counting the number of CFU at each time point. Asterisks indicate the time points when the intracellular bacteria survival rates elicited by the ΔhylB mutant were significantly lower (P < 0.05) than those produced by wild-type infection. (B) RAW264.7 macrophages were infected with different numbers of cells of the S. agalactiae GD201008-001 wild-type (WT), mutant (ΔhylB), and complemented (CΔhylb) strains. At 1 h postinfection, cells were extensively washed to remove extracellular bacteria after antibiotic treatment and were lysed; CFU were then measured. The data shown are means ± SEM from three independent experiments.