Figure 5. Internalization and persistence of bimBm and bimBp 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 bimBm and bimBp 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 bimBp, the percentage of leukocytes positive for intracellular BpOMP was significantly higher in cultures stimulated with bimBm isolates at 24 hours postinfection. Internalization of bimBm or bimBp isolates by CD11c+ dendritic cells and F4/80+ macrophages was comparable (not shown). C) However, persistence of bimBm 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.