CULTIVATION OF EHRLICHIA-CHAFFEENSIS IN MOUSE EMBRYO, VERO, BGM, AND L929 CELLS AND STUDY OF EHRLICHIA-INDUCED CYTOPATHIC EFFECT AND PLAQUE-FORMATION

We successfully propagated Ehrlichia chaffeensis in mouse embryo, Vero , BGM, and L929 cells inoculated with host cell-free ehrlichiae, indic ating that E. chaffeensis is capable of entry, survival, and growth in a relatively wide range of cell types derived from different species, We demonstrated rapid adaptation of E. chaffeensis in these cell line s, so that typical morulae could be detected as early as 5 days after inoculation, E. chaffeensis-induced cytopathic effect with different m orphological characteristics in mouse embryo, Vero, and L929 cells, Th e earliest cytopathic effect appeared in untreated and irradiated mous e embryo cells at 4 days postinoculation, As the infected foci gradual ly expanded, the center of the foci showed necrotic cells with pyknoti c nuclei and degraded morulae, E. chaffeensis caused cell lysis in unt reated and irradiated L929 cells, with formation of distinct, round ma croscopic plaques at 18 days postinoculation, In untreated and irradia ted Vero cells, E. chaffeensis produced infected foci composed of loos ely interwoven necrotic cells, spaces of detached cells, cells filled with morulae, and uninfected cells, resulting in characteristic reticu lar foci, Irradiated cells generally contained many large morulae and presented larger cytopathic foci, DH82 and BGM cells did not develop o bvious cytopathic foci under the conditions employed, The findings rep orted herein offer the opportunity to study the pathogenic mechanism o f cell injury by E. chaffeensis, the basis for quantification of infec tious E. chaffeensis, improved approaches for recovery of ehrlichiae f rom human patients and tick hosts,and additional methods for cultivati on of E. chaffeensis for molecular analysis,