Molecular evidence for novel chlamydial infections in the koala (Phascolarctos cinereus)
Devereux, LN, Polkinghorne, A, Meijer, A & Timms, P 2003, Systematic and Applied Microbiology, vol. 26, pp. 245-253.
Infection with Chlamydia is common in wild koalas. C. pecorum and C. pneumoniae largely infect the eye, the genitourinary tract and the respiratory system of the koala. In this study, a commonly used method of polymerase chain reaction (PCR) was used to detect nine novel Chlamydia-like strains infecting koalas. A new technique using fragments of ribosomal RNA (rRNA) gene was developed to further evaluate these additional strains.
In 1999, 94 swabs from 25 koalas were taken and, of these, 72% had a chlamydial infection with C. pecorum (52%), C. pneumoniae (12%), and/or an unidentifiable strain (16%). In 2000, 126 swabs from 36 koalas were taken and, of these, only 36% had a chlamydial infection with C. pecorum (22%) and/or C. pneumoniae (17%). Chlamydial infections were identified using an established PCR test targeting the 16S rRNA gene. Fragments of 16S rRNA gene, labelled uncultured koala Chlamydiales or UKC, were sequenced to identify the unknown chlamydial strains. Nine new sequences were identified and labelled UKC1-9. rRNA folding of UKC sequences was checked and determined to be genuine. One hundred and fifty-seven sequences of UKC1-9 sequences were analysed against known Chlamydiales order sequences using phylogenetic analysis. UKC sequences appeared to form a separate group from Chlamydia genera and had similarities with other unidentified Chlamydia-like sequences. UKC7 was the only sequence that was similar to an identified Chlamydia-like bacterium, endosymbiont of Acanthamoeba sp. UWE1. UKC3-UKC6 were most similar to each other. PCR was used to amplify UKC sequences using a set of primers, a piece of genetic code used to start a PCR, UCK-A and UCK-B. The primers detected most UKC variants in the study, except UKC1, UKC2, UKC8 and UKC9, and did not detect any of the known Chlamydia species. The PCR method was tested on 25 koalas with chlamydia: 72% has UKC-A and 24% had UKC-B sequences. Coinfections of UKC-A and UKC-B with C. pecorum and C. pneumoniae were common.
rRNA folding of some UKC sequences had mispairings and this is likely due to natural sequence variation. Previous analyses may have missed these variations by using pre-determined primers. Phylogenetic analysis revealed that UKC sequences belong to another group of bacteria, similar to Chlamydia, that did not fall into the established Chlamydia and Chlamydophila genera nor into Chlamydia-like families of Parachlamydiaceae, Simkaniaceae, or Waddliaceae. It is unclear if UKC type A (UKC3, UKC4, UKC5 and UKC6) and UCK type B (UKC7) bacteria are responsible for causing disease in koalas, as they were found to co-occur with known pathogens C. pecorum and C. pneumoniae.
This study has contributed to our knowledge of Chlamydia and Chlamydia-like species and described nine new bacteria that should be placed into a Chlamydia-like family affecting koalas. Future work should concentrate on sequencing the whole rRNA gene in order to identify all bacteria that may belong to Chlamydiales order, which may in turn inform infection and disease management approaches.
Summarised by Alexandra Selivanova
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