Emended description of the order Chlamydiales, proposal of Parachlamydiaceae fam. nov. and Simkaniaceae fam. nov., each containing one monotypic genus, revised taxonomy of the family Chlamydiaceae, including a new genus and five new species, and standards for the identification of organisms

The current taxonomic classification of Chlamydia is based on limited pheno typic, morphologic and genetic criteria. This classification does not take into account recent analysis of the ribosomal operon or recently identified obligately intracellular organisms that have a chlamydia-like developmenta l cycle of replication. Neither does it provide a systematic rationale for identifying new strains. In this study, phylogenetic analyses of the 16S an d 23S rRNA genes are presented with corroborating genetic and phenotypic in formation to show that the order Chlamydiales contains at least four distin ct groups at the family level and that within the Chlamydiaceae are two dis tinct lineages which branch into nine separate clusters. In this report a r eclassification of the order Chlamydiales and its current taxa is proposed. This proposal retains currently known strains with >90% 16S rRNA identity in the family Chlamydiaceae and separates other chlamydia-like organisms th at have 80-90% 16S rRNA relatedness to the Chlamydiaceae into new families. Chlamydiae that were previously described as 'Candidatus Parachlamydia aca nthamoebae' Amann, Springer, Schonhuber, Ludwig, Schmid, Muller and Michel 1997, become members of Parachlamydiaceae fam. nov., Parachlamydia acantham oebae gen. nov., sp. nov. 'Simkania' strain Z becomes the founding member o f Simkaniaceae fam. nov., Simkania negevensis gen. nov., sp. nov. The fourt h group, which includes strain WSU 86-1044, was left unnamed. The Chlamydia ceae, which currently has only the genus Chlamydia, is divided into two gen era, Chlamydia and Chlamydophila gen. nov. Two new species, Chlamydia murid arum sp. nov, and Chlamydia suis sp. nov., join Chlamydia trachomatis in th e emended genus Chlamydia. Chlamydophila gen. nov. assimilates the current species, Chlamydia pecorum, Chlamydia pneumoniae and Chlamydia psittaci, to form Chlamydophila pecorum comb. nov., Chlamydophila pneumoniae comb. nov. and Chlamydophila psittaci comb. nov. Three new Chlamydophila species are derived from Chlamydia psittaci: Chlamydophila abortus gen. nov., sp. nov., Chlamydophila caviae gen, nov., sp. nov. and Chlamydophila felis gen. nov. , sp. nov. Emended descriptions for the order Chlamydiales and for the fami ly Chlamydiaceae are provided. These families, genera and species are readi ly distinguished by analysis of signature sequences in the 16S and 23S ribo somal genes.