This diagram is adapted from Roux and Raoult (1), although not to scale. It shows the phylogenetic classification of the genus Rickettsia based upon sequence comparisons of OmpB genes. The colored boxes enclose monophyletic groups or clades within the genus. For more information on the various species, click on the appropriate blue dot adjacent to the species name.

Although MIF testing has been the serologic gold standard, orginally being the means of determining separate species, the main obstacle is their common lipopolysaccharide (LPS) antigen. As all of the spotted fever group share the same LPS antigen, the effect of differences in OmpB reactivity is diminished  when testing for IgG-class antibody and leads to false-positives when testing for IgM-class antibody. We are currently making custom antigen panels (native Omp A and/or OmpB) available to detect species-specific responses.  Call or email for details.

Additions to collection:

Rickettsia amblyommii was placed within the blue-outlined clade on the basis of OmpB sequence comparison.

Rickettsia monacensis is located in a separate clade between the green-outlined and yellow-outlined clades with Rickettsia buchneri, a tick endosymbiont (2).

1) Roux, V. & D. Raoult, 2000. Phylogenetic analysis of members of the genus Rickettsia using the gene encoding the outer-membrane protein rOmpB (ompB). Int. J. Syst. Evol. Microbiol. 50: 1449-1455.

2)  Kurtii, T., R. Felsheim, N. Burkhardt, J. Oliver, C. Heu and U. Munderloh, 2015. Rickettsia buchneri sp. nov., a rickettsial endosymbiont of the blacklegged tick Ixodes scapularis. Int J Sys Evol Microbiol 65: 965-970.