Phylogenetic analysis of the genus Chlamydia based on 16S rRNA gene sequences

The phylogenetic relationships among Chlamydia spp. were investigated by comparing 16S rRNA gene sequences. In this analysis we used 14 strains of Chlamydia psittaci, including seven feline isolates, two avian isolates, two human isolates, one bovine isolate, one ovine isolate, and one guinea pig isolate; five strains of Chlamydia pecorum, including three bovine isolates, one ovine isolate, and one koala isolate; and nine strains of Chlamydia trachomatis, including six human isolates, two swine isolates, and one mouse isolate. A phylogenetic analysis of the 16S rRNA gene sequences of these organisms and seven previously published sequences revealed eight genetic groups which formed two clusters. The first cluster was composed of C. pecorum, Chlamydia pneumoniae, and C. psittaci and included three genetic groups (one group containing avian: human, and ovine strains, one group containing feline strains, and one group containing guinea pig strains). The second cluster was composed of C. trachomatis and also included three genetic groups (one group containing human strains, one group containing swine isolates, and one group containing rodent strains). The strains in each genetic group exhibited similar genetic distances. The results of the phylogenetic analysis agreed with the results of previous genomic DNA, ompA gene allele, and biotyping studies. Therefore, the genetic groups based on genetic distances may be considered a criterion for species identification.