An investigation of streptococcal flora in faeces of koalas
Osawa, RO 1991, Journal of Wildlife Management, vol. 55, no. 4, pp. 623-627.
The occurrence, counts and biochemical characteristics of streptococcal flora in koala faeces differ according to sex and living environment. Female koalas have approximately ten times more of the tannin-protein complex degrading (T-PCD) Streptococcus bovis bacterium in their faeces than males. Strains of T-PCD S. bovis were not only more dominant among the faecal streptococcal of free-ranging koalas than of captive koalas but were also biochemically unique between each group. The enterococci S. faecalis and S. faecium were found only in the faeces of captive koalas, indicating that the bacteria were spread from humans or other animals.
Tannins are biomolecules that bind to proteins to form chemical complexes and typically exist in eucalypts in high concentrations. The tannin-protein complexes are highly resistant to degrading in the gut of a mammal and consequently disrupt the digestion of dietary proteins. The S. bovis bacterium, which is capable degrading the tannin-protein complexes, is therefore important for digestion in the koala, which feeds on Eucalyptus foliage.
Many of the female koalas sampled in this study were lactating, and therefore it is likely that females have significantly higher viable counts of T-PCD S. bovis in their alimentary tracts than males to account for their greater metabolic need for dietary protein while caring for their young. The greater occurrence of the T-PCD S. bovis bacterium in the faeces of free-ranging koalas than in that of captive koalas may relate to the contrasting diets of each group. Captive koalas might require less of the bacterium as they are typically offered a large range of Eucalyptus species on which to feed and may therefore preferentially select species with relatively lower tannin concentrations. Free-ranging koalas, on the other hand, are restricted in their choice of food species and may therefore rely on microbiological defence against the degradation-resistant tannins. The strains of T-PCD S. bovis in the faeces of koalas were biochemically unique to either a captive or free-ranging environment. Interestingly, the biochemical characteristics of S. bovis isolated from free-ranging koalas were similar to those from koalas that had been in captivity for three years or less. This finding demonstrates that some T-PCD S. bovis strains can be harboured in the alimentary tract for a considerable length of time and even transferred to young koalas via ‘pap’ feeding.
As well as improving our understanding of the feeding practices and dietary mechanisms of koalas both in the wild and in captivity, the findings of this study suggest that enterococci other than S. bovis can be used as ‘indicator’ organisms to evaluate the degree of contamination of areas inhabited by koalas by other species, including humans.
Summarised by Joanna Horsfall
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