Figure 8

Macrophage infection assay with E. coli Top10F', R. equi USA-18, and R. equi USA-18ΔB8. Macrophages derived from the human THP-1 cell line were infected with the indicated bacteria at a multiplicity of infection of 10 as described in Materials and methods. The number of intracellular bacteria within the macrophages was determined by plate counting at 4, 24, and 96 h post-infection.