Abstract
A chlamydial plasmid, 6.2 kb in size, was isolated from an avian strain of Chlamydia psittaci and cloned into the EcoRI site of pUC13. A restriction enzyme cleavage map of the resultant clone, pAP1p, was very similar to the published map of the plasmid cloned from the C. psittaci meningopneumonitis strain Cal-10. Southern hybridisation analyses using pAP1p as a probe, revealed the presence of plasmids with homologous DNA sequences in avian psittacosis, avian ornithosis, ovine polyarthritis and sporadic bovine encephalomyelitis strains of C. psittaci, as well as the LGV strain of Chlamydia trachomatis. Plasmid was not detected in koala conjunctivitis, ovine abortion or feline conjunctivitis isolates. The plasmid-containing isolates could be grouped according to size (6.2 or 7.2–7.3 kb) and restriction endonuclease pattern. These three plasmid categories correlate with previously reported C. psittaci biotypes, immunotypes and serotypes. The absence of plasmid from three infectious, pathogenic strains of C. psittaci suggests that, in this species at least, plasmid-encoded genes are not essential for survival, infectivity or virulence of the parasite.
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