Comparison of Properties of Isolated Ehrlichiae and Scrub Typhus Rickettsiae.

摘要

A great deal have been learned during the past few years about the position of some of the rickettsiae in the microbial world. Comparisons of 16S rRNA nucleotide sequences indicate that the trench fever rickettsia, Rochalimaea quintana, belongs in the alpha subdivision of the purple bacteria. Within this group, R. quintana is specifically related to the agrobacteria and rhizobacteria. Three species of the genus Rickettsia, namely R. prowazekii, R. typhi, and R. rickettsii, form a very close cluster, which is also located in the alpha subdivision. Surprisingly, these rickettsiae are not specifically related to the trench fever agent, despite their significant DNA-DNA homology. Instead, they are specifically, although somewhat distantly, related to Ehrlichia risticii. This is also surprising, since there are considerable phenotypic differences between rickettsiae and ehrlichiae. Coxiella burnetii is not related to either the typhus or spotted fever groups in the genus Rickettsia. It belongs in the gamma subdivision of the purple bacteria, where it is distantly but specifically related to Legionella. (TTL)