For macrophage growth assays, 96well
microtiter plates were seeded with 2×10
macrophages/well and infected with B. abortus 544 at a ratio of 1:100 bacteria/macrophage. Cells were incubated
for one h at 37°C in 5% CO . Extracellular bacteria were removed by three washes with PBS, followed by
treatment with 25 μg/ml of gentamicin for 30 min.