Rickettsia felis: molecular characterization of a new member of the spotted fever group

In this report, placement of Rickettsia felis in the spotted fever group (S FG) rather than the typhus group (TC) of Rickettsia is proposed. The organi sm, which was first observed in cat fleas (Ctenocephalides felis) by electr on microscopy, has not yet been reported to have been cultivated reproducib ly, thereby limiting the standard rickettsial typing by serological means. To overcome this challenge, several genes were selected as targets to be ut ilized for the classification of R. felis. DNA from cat fleas naturally inf ected with R. felis was amplified by PCR utilizing primer sets specific for the 190 kDa surface antigen (rOmpA) and 17 kDa antigen genes. The entire 5 513 bp rompA gene was sequenced, characterized and found to have several un ique features when compared to the rompA genes of other Rickettsia. Phyloge netic analysis of the partial sequence of the 17 kDa antigen gene indicated that R. felis is less divergent from the SFG rickettsiae than from the TG rickettsiae, The data corroborate results from previous reports that analys ed the citrate synthase, 165 rRNA, rompB (135 kDa surface antigen), metK, f tsY, polA and dnaE genes that placed R. felis as a member of the SFC. The o rganism is passed trans-stadially and transovarially, and infection in the cat flea has been observed in the midgut, tracheal matrix, muscle, hypoderm is, ovaries and testes.