Plaque Formation by Rickettsia conori in WI-38, DBS-FRhL-2, L-929, HeLa, and Chicken Embryo Cells.

Mammalian cells particularly suitable for the study of specialized aspects of rickettsial biology were tested for their ability to support plaque formation by Rickettsia conori. The detection of plaques was substantially influenced by the combination of growth medium and cell type used. Large plaques (2.0 to 3.0 mm in diameter) occurred by 8 days postinfection in WI-38 and DBS-FRhL-2 cells supported by medium 199. Smaller plaques (0.5 to 1.0 mm in diameter) were seen in L-929 and HeLa cells at 8 to 11 days postinfection and were more discernible in cells supported with Eagle minimal essential medium. Chicken embryo cells maintained in Dulbecco's modified Eagle medium exhibited large spherical plaques with a diameter of approximately 1.5 mm by 8 days postinfection.