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Outer membrane protein 2 gene sequences indicate that Chlamydia pecorum and Chlamydia pneumoniae cause infections in koalas

Glassick, T, Giffard, P & Timms, P 1996, Systematic and Applied Microbiology, vol. 19, no. 1, pp. 457-464.

Seven strains of Chlamydia present in koalas that were all previously described as types of Chlamydia psittaci have been reclassified as either C. pneumoniae or C. pecorum following genetic sequence and phylogenetic analyses.

  The DNA sequences of segments of the ‘outer membrane protein (omp) 2’ gene from seven strains of Chlamydia of koala origin were compared with previously reported gene sequences and those of other strains from various origins. The koala chlamydial strains could be divided into two distinct genetic groups. The first, koala omp 2 group A, was previously classified as C. psittaci type I. The authors proposed that this strain be termed C. pneumoniae given its 99% similarity to a strain of human and a strain of horse C. pneumoniae. The second strain, koala omp 2 group B, was previously classified as C. psittaci type II but was here proposed to be reclassified as C. pecorum as its genetic sequence was found to be 99% similar to this strain.

  Chlamydia is one of the greatest threats to the survival of free-ranging koala populations, causing a variety of symptoms including conjunctivitis, rhinitis, urinary tract disease and infertility. Given the prevalence of this threat, it is important to understand the epidemiology of koala chlamydial infections. Previously, chlamydial strains in koalas were described solely as Chlamydia psittaci due to the pathogen’s broad mammalian host range, and subsequently divided into types I and II. These understandings, however, were based on studies that included only single strains from koalas, from a single gene, and with poorly documented origins. The purpose of this study was to test these previously asserted genetic relationships and improve epidemiological descriptions of koala chlamydial strains by analysing a greater number of strains and DNA sequence data from an alternative genomic locus.

  The findings of this study demonstrate that chlamydial infections in koalas may be attributable to more than one strain of Chlamydia, and may be significant in the development of vaccines effective for combating this complex disease.

 

Summarised by Joanna Horsfall

 

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