Abstract
FL cell cultures infected with the Nakazaki strain of Rickettsia sennetsu were studied. The rickettsiae propagated themselves in the FL cells for a long period of time without interfering with host cell growth. The infected culture has been successively subcultured to establish the persistent infection of rickettsia in vitro. The persistence of the rickettsia in the cultures has been confirmed at each transfer by microscopic examination and by titration in mice.
The rickettsia in this system had retained their infectivity for mice and FL cells. However, the death of mice inoculated with the rickettsia carried in vitro, was remarkably prolonged as the number of transfer incerased.
The study characterized the mutual co-existence of host cells and rickettsiae. The balanced multiplication of them might have enabled the FL cell culture to remain persistently infected. The role of cell-to-cell infection, as well as division of infected cell, was discussed in relation to the establishment of persistent rickettsial infection in vitro.
