FIG. 1.

Intracellular survival of T. whipplei. (A) HeLa cells were infected with T. whipplei (bacterium-to-cell ratio, 50:1) for different periods. (B) Cells were infected with different concentrations of T. whipplei for 4 h. (C) Cells were infected with T. whipplei (bacterium-to-cell ratio, 50:1) for 4 h, washed to remove free bacteria, and incubated for different additional periods. Bacteria were revealed by indirect immunofluorescence, and the infection index was determined. The viability of intracellular bacteria was studied using a combination of SYTO 9 and propidium iodide; the results are expressed as percentages of viable bacteria. The results represent the mean ± SD of four experiments.