EVIDENCE FOR CHLAMYDIA-PNEUMONIAE OF NONHUMAN ORIGIN

This paper describes the characterization and taxonomic status of N16, a chlamydial isolate from the respiratory tract of a horse. N16 conta ins plasmid DNA, has normal elementary body morphology and its inclusi ons do not stain with iodine. Its major outer-membrane protein (MOMP) gene was completely sequenced and compared with the MOMP genes of Chla mydia pneumoniae, C. psittaci, C. trachomatis and C pecorum. This anal ysis revealed that N16 is closely related to the TWAR strain of C pneu moniae (94.5 % and 94.4 % DNA homology with TWAR isolates IOL-207 and AR-39 respectively). By comparison, N16 shows between 72.1 % and 73.7 % DNA homology with C. psittaci strains, 70.9 % and 71.1 % homology wi th C. pecorum strains LW613 and 1710S and 69.2 % homology with C. trac homatis serotype E. The MOMP gene of N16 shares 93-8 % DNA homology wi th the MOMP gene of a chlamydial isolate KC from the conjunctiva of a koala. Monoclonal antibodies raised to C. pneumoniae IOL-207 and shown to be C. pneumoniae-specific confirmed that N16 was more closely rela ted to C. pneumoniae than to C. psittaci. Thus DNA homology and monocl onal antibody data both suggest that horse chlamydiae, as exemplified by N16, form a new second strain of C. pneumoniae. This species is pro bably more widespread and diverse than the current literature would su ggest.