Fig. 3.

Serial photographs of infected ECV304 cells in medium containing doxycycline (see Fig. 1 for details) (×200). Doxycycline at 40 and 80 µg/mL was toxic, resulting in death of ECV304 cells. In the Boryong strain-infected cells, the highest doxycycline concentrations at which IF-positive foci are observed are 10, 20, and 20 µg/mL on days 5, 13, and 28, respectively. In the AFSC-4 strain-infected cells, the highest concentration is 20 µg/mL on days 5, 13, and 28. Cultures infected with the AFSC-4 strain in medium containing 0.1 µg/mL doxycycline showed cell death because of overgrowth of O. tsutsugamushi on day 20.