TABLE 1.
Agent | Vacuolar pH | Cell viability (%) | Cell infection |
---|---|---|---|
Control | 4.7 ± 0.3 | 98 ± 2 | 696 ± 32 |
NH4Cl (100 nM) | 6.45 ± 0.15 | 85 ± 6 | 70 ± 12∗ |
N-Ethylmaleimide (25 mM) | 6.35 ± 0.2 | 87 ± 5 | 108 ± 15∗ |
Bafilomycin A1 (0.1 nM) | 6.5 ± 0.15 | 90 ± 4 | 81 ± 11∗ |
Chloroquine (2 mM) | 6.35 ± 0.2 | 89 ± 6 | 37 ± 8∗ |
HeLa cells were incubated with T. whipplei (bacterium-to-cell ratio, 100:1) for 4 h and then with pH-neutralizing drugs for 48 h. The vacuolar pH was measured by ratiometric analysis of DM-NERF fluorescence intensities, and mean pH values were calculated using a pH reference curve. The cell viability was determined by trypan blue exclusion. Intracellular bacteria were revealed by indirect immunofluorescence, and their viability was assessed by using a combination of SYTO 9 and propidium iodide. The infection by viable organisms was expressed as the mean index (absolute value of infection index) ± SD of three experiments. ∗, P < 0.01.