Isolation of a spotted fever group rickettsia, Rickettsia peacockii, in a Rocky Mountain wood tick, Dermacentor andersoni cell line

An embryonic cell line (DAE100) of the Rocky Mountain wood tick, Dermacento r andersoni, was observed by microscopy to be chronically infected with a r ickettsialike organism, The organism was identified as a spotted fever grou p (SFG) rickettsia by PCR amplification and sequencing of portions of the 1 6S rRNA, citrate synthase, Rickettsia genus-specific 17-kDa antigen, and SF G-specific 190-kDa outer membrane protein A (rOmpA) genes. Sequence analysi s of a partial rompA gene PCR fragment and indirect fluorescent antibody da ta for rOmpA and rOmpB indicated that this rickettsia was a strain (DaE100R ) of Rickettsia peacockii, an SFG species presumed to be avirulent for both ticks and mammals, R, peacockii was successfully maintained in a continuou s culture of DAE100 cells without apparent adverse effects on the host cell s. Establishing cell lines from embryonic tissues of ticks offers an altern ative technique for isolation of rickettsiae that are transovarially transm itted.