CYTOPATHIC EFFECT, PLAQUE-FORMATION, AND LYSIS OF EHRLICHIA-CHAFFEENSIS GROWN ON CONTINUOUS CELL-LINES

Ehrlichiae are strict intracellular bacterial pathogens that parasitiz e leukocytes or other blood cells. Only six agents of the tribe Ehrlic hieae, namely, Cowdria ruminantium, Neorickettsia helminthoeca, Ehrlic hia risticii, Ehrlichia sennetsu, Ehrlichia canis, and Ehrlichia chaff eensis, have been adapted to growth in continuous cell lines. E. chaff eensis, the agent of human ehrlichiosis, has been cultured only in a c ell line of canine origin. We adapted purified cell-free E. chaffeensi s for growth in human embryonic lung (HEL) fibroblasts (HEL 299), gree n monkey kidney cells (Vero), and a human cervical epithelioid carcino ma (HeLa) cell line. We observed a cytopathic effect with both Vero ce lls and HEL cells and plaque formation with cellular lysis when infect ed Vero cells were cultured in agar. Human fibroblasts are already com monly used for the isolation of viruses, coxiellae, and rickettsiae. F urthermore, the capability of these cells to support the growth of ehr lichiae suggests that they may be useful for primary isolation of ehrl ichiae as well. The cytopathic effect produced in Vero or HEL cells of fers a very helpful indicator of the infection. Plaque formation in Ve ro cells is a new phenomenon not Set reported for ehrlichiae and will allow the titration of inocula and clonal purification of this bacteri um.