Genetic diversity of avian and mammalian Chlamydia psittaci strains and relation to host origin.

Genetic relationships were reported for Chlamydia psittaci derived from psittacine birds, pigeons, turkeys, humans, cats, muskrats, cattle, and sheep and for C. trachomatis, including representative strains of the three biovars, through physical analysis of genomic DNA including DNA fingerprinting with restriction endonuclease SalI, DNA-DNA hybridization in solution with S1 nuclease, and Southern analysis with genomic DNA probes. A total of 26 strains were divided into four groups of C. psittaci and two groups of C. trachomatis, on the basis of DNA fingerprints. The six groups of Chlamydia spp. were related to host origin: two avian groups (Av1 and Av2), one feline and muskrat group (Fe1), one ruminant group (Ru1), one C. trachomatis biovars trachoma and lymphogranuloma group (CtHu), and one C. trachomatis mouse biovar group (CtMo), although an ovine abortion strain belonged to the avian group Av2. DNA-DNA hybridization assay and Southern analysis with genomic DNA probes indicated three DNA homology groups in the genus Chlamydia: an avian-feline group (groups Av1, Av2, and Fe1), a ruminant group (group Ru1), and a C. trachomatis group (groups CtHu and CtMo). Furthermore, the Southern analysis indicated that the homologous sequences (DNA homology of at least 14%) within the avian-feline group were distributed along the whole genome, whereas the homologous sequences (DNA homology of less than 24%) among the three DNA homology groups were localized in distinct regions of the genome DNA. These results suggest that Chlamydia spp. are derived from a common ancestor and have diverged into various groups showing restricted host ranges as a natural characteristic and that the species C. psittaci should be differentiated into groups related to host origin and DNA homology.