Microbiota composition of the koala (Phascolarctos cinereus) ocular and urogenital sites, and their association with Chlamydia infection and disease
Vidgen, ME, Hanger, J & Timms P 2017, Scientific Reports, vol. 7, article 5239
This study explored the potential associations between microbiota profiles at penile/urogenital and ocular sites, chlamydial infection status, and demographic factors in free-ranging koalas. It was found that the presence or absence of particular microbiota in the female urogenital tract may contribute to the progression of Chlamydia pecorum infection to disease at the site. Penile and urogenital tract microbiota, but not ocular microbiota, were also found to differ between the sexes and life stages.
The most common phyla among microbiota detected at urogenital and ocular sites in the koala were Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes and Acidobacteria. Of these, the most dominant were Aerococcus-like organisms from the order Lactobacillales and the phylum Firmicutes. Compared to the urogenital tract and penile microbiota, ocular microbiota in the koala was found to be of lower abundance but higher diversity. No single organism dominated the ocular sites. In the urogenital tract, pregnancy was strongly associated with a reduction in the overall diversity of the microbiome, an increase of two microbiotas, and a shift in the dominant Lactobacillales organism. These changes may stem from microbes introduced to the urogenital canal from the upper-genital tract during formation of the pseudo-vaginal canal that occurs during pregnancy. In males, changes in penile microbiota were associated with age. Sub-adult males were observed to have less rich and less diverse microbiota than adult and senior males. Similar findings in humans indicate that these differences may relate to sexual maturity and experience. The authors detected a correlation between microbiota composition and level of C. pecorum infection in the female urogenital tract. Different levels of infection were associated with specific microbiota profiles, which suggests that particular organisms of the microbiota may contribute to the acceleration or prevention of the chlamydial infection progressing to disease. Some Chlamydia-like organisms were detected in this study, though none were thought to contribute to chlamydial disease which is caused primarily by C. pecorum.
Chlamydial infection and disease are widespread in free-ranging koala populations. As well as causing blindness, infertility and even death, the threat reduces the ability for koalas to cope with other pressures associated with habitat decline and fragmentation. The factors that may contribute to the progression or otherwise of C. pecorum infection are poorly understood but may include pathogen strain diversity, koala immune capability, environmental factors, and host microbiota. In other hosts, the presence of particular microbiotas has been found to influence the progression of particular infections to disease. With Chlamydia being one of those infections, given the threat that C. pecorum poses to koalas, this investigation into organisms that may co-occur with the pathogen was warranted.
As well as being the first study to examine the microbiota of the koala urogenital tract, its findings indicate that particular biological variables and microbiota profiles may be implicated in the acceleration or prevention of the progression of chlamydial infection to disease. As a result, the authors emphasise the importance of studies that employ a ‘whole system’ approach to investigating chlamydiosis in koalas.
Summarised by Joanna Horsfall
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