Summary auto-generated
This article presents a major taxonomic reorganization of bacteria in the families Rickettsiaceae and Anaplasmataceae based on genetic and molecular analyses. The authors analyzed 16S rRNA gene and groESL operon sequences from multiple obligate intracellular bacteria, identifying four distinct genetic clusters. Their phylogenetic analyses revealed that existing taxonomic classifications were not supported by molecular data. Key reorganizations include: merging Ehrlichia phagocytophila, Ehrlichia equi, and the human granulocytic ehrlichiosis (HGE) agent into a single species (now Anaplasma phagocytophila); moving Cowdria ruminantium into the genus Ehrlichia; and expanding Neorickettsia to include Ehrlichia risticii and Ehrlichia sennetsu. The authors propose that members of the tribes Ehrlichieae and Wolbachieae be transferred to the expanded family Anaplasmataceae. This reorganization is supported by sequence similarities, groESL data, antigenic analyses, and biological characteristics including host cell tropism and vector associations. These changes unify species with greater than 96% genetic similarity into appropriate genera while maintaining distinctions between the four major clusters identified in their analysis.
Key findings
- Four distinct genetic clusters were identified among Anaplasma, Ehrlichia, Cowdria, Neorickettsia, and Wolbachia species based on 16S rRNA and groESL sequence analyses.
- Ehrlichia phagocytophila, Ehrlichia equi, and the HGE agent share >98% 16S rRNA similarity and should be recognized as a single species (Anaplasma phagocytophila).
- Cowdria ruminantium should be reclassified as Ehrlichia ruminantium based on genetic and phenotypic characteristics.
- The family Anaplasmataceae should be expanded to include reorganized members of Ehrlichia, Anaplasma, Cowdria, Wolbachia, and Neorickettsia genera, while Rickettsiaceae remains composed of Rickettsia and Orientia.
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
The genera Anaplasma, Ehrlichia, Cowdria, Neorickettsia and Wolbachia encompass a group of obligate intracellular bacteria that reside in vacuoles of eukaryotic cells and were previously placed in taxa based upon morphological, ecological, epidemiological and clinical characteristics. Recent genetic analyses of 16S rRNA genes, groESL and surface protein genes have indicated that the existing taxa designations are flawed. All 16S rRNA gene and groESL sequences deposited in GenBank prior to 2000 and selected sequences deposited thereafter were aligned and phylogenetic trees and bootstrap values were calculated using the neighbour-joining method and compared with trees generated with maximum-probability, maximum-likelihood, majority-rule consensus and parsimony methods. Supported by bootstrap probabilities of at least 54%, 16S rRNA gene comparisons consistently clustered to yield four distinct clades characterized roughly as Anaplasma (including the Ehrlichia phagocytophila group, Ehrlichia platys and Ehrlichia bovis) with a minimum of 96.1% similarity, Ehrlichia (including Cowdria ruminantium) with a minimum of 97.7% similarity, Wolbachia with a minimum of 95.6% similarity and Neorickettsia (including Ehrlichia sennetsu and Ehrlichia risticii) with a minimum of 94.9% similarity. Maximum similarity between clades ranged from 87.1 to 94.9%. Insufficient differences existed among E. phagocytophila, Ehrlichia equi and the human granulocytic ehrlichiosis (HGE) agent to support separate species designations, and this group was at least 98.2% similar to any Anaplasma species. These 16S rRNA gene analyses are strongly supported by similar groESL clades, as well as biological and antigenic characteristics. It is proposed that all members of the tribes Ehrlichieae and Wolbachieae be transferred to the family Anaplasmataceae and that the tribe structure of the family Rickettsiaceae be eliminated. The genus Anaplasma should be emended to include Anaplasma (Ehrlichia) phagocytophila comb. nov. (which also encompasses the former E. equi and the HGE agent), Anaplasma (Ehrlichia) bovis comb. nov. and Anaplasma (Ehrlichia) platys comb. nov., the genus Ehrlichia should be emended to include Ehrlichia (Cowdria) ruminantium comb. nov. and the genus Neorickettsia should be emended to include Neorickettsia (Ehrlichia) risticii comb. nov. and Neorickettsia (Ehrlichia) sennetsu comb. nov.