Figure 5. Internalization and persistence of bim_Bm and bim_Bp Burkholderia pseudomallei isolates within murine leukocytes. Spleen and lymph node–derived leukocytes were co-cultured with B. pseudomallei isolates at multiplicity of infection 1:5. A) At 2, 8, and 24 hours postinfection, absolute numbers of CD45⁺ leukocytes were comparable in cultures infected with bim_Bm and bim_Bp strains. B) Bacterial uptake (2 h) and persistence (8 h and 24 h) was compared by assessing the percentage of CD45⁺ leukocytes that were positive for intracellular B. pseudomallei outer membrane protein antibody (BpOMP) staining using flow cytometry. BpOMP staining increased within leukocytes between 8 hours and 24 hours of cultures. Compared with bim_Bp, the percentage of leukocytes positive for intracellular BpOMP was significantly higher in cultures stimulated with bim_Bm isolates at 24 hours postinfection. Internalization of bim_Bm or bim_Bp isolates by CD11c⁺ dendritic cells and F4/80⁺ macrophages was comparable (not shown). C) However, persistence of bim_Bm strains was significantly higher in dendritic cells and macrophages after 24 hours of culture. Data reflect the mean +SD of 2 independent experiments. BpOMP, B. pseudomallei outer membrane protein antibody; DC, dendritic cells; Mϕ, macrophages. *p<0.05; **p<0.01; ***p<0.001.