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Tannin-protein complex-degrading enterobacteria isolated from the alimentary tracts of koalas and a selective medium for their enumeration

Osawa, RO 1992, Applied and Environmental Microbiology, vol. 58, no. 5, pp. 1754-1759.

Strains of tannin-protein complex degrading (T-PCD) bacteria were identified in the faeces and caecum of the koala. These enterobacteria were facultatively anaerobic, gram-negative, pleomorphic, nonmotile bacilli, which are characteristics indicating that the strains fell within the Enterobacteriaceae family. All strains formed distinctly separate colonies after incubation on a tannin-treated agar plate and were also resistant to the antibiotic vancomycin. These characteristics informed the development of a selective agar plate medium that could be used to isolate and identify T-PCD enterobacteria from koala faeces while simultaneously restricting the growth of the common T-PCD bacterium Streptococcus bovis.

  Tannins are biomolecules that bind to proteins to form chemical complexes and typically exist in eucalypts in high concentrations. Koalas, therefore, require a mechanism to ‘degrade’ these complexes to extract the protein for metabolism. The tannin-protein complex degrading S. bovis bacterium has previously been reported as the dominant streptococcal flora in the faeces of the koala and is able to separate the protein component of the tannin-protein complex; however, the potential roles of other bacteria in this degradation process were previously unknown. The T-PCD enterobacteria described in this investigation were isolated from a bacterial layer of the koala’s caecal wall, indicating that they play an important role in degrading tannin-protein complexes in the alimentary tract to harness their dietary proteins for metabolic use. In addition, the T-PCD enterobacteria had viable counts far greater than those of the bacterium S. bovis in most samples, which suggests that their role in the digestion of eucalypt leaves is greater than that of S. bovis. These T-PCD endobacteria may remain securely attached to the caecal wall by the ‘bacterial layer’ observed in this study, with only dead or unsecured microbes flushed into the colon, which would explain their absence in some of the faecal samples.

  The characteristics of the T-PCD enterobacteria isolated from the samples enabled the production of an effective selective medium (Wilkins-Chalgren anaerobe agar treated tannic acid solution and containing vancomycin hydrochloride) for the enumeration of T-PCD enterobacteria strains in faecal samples. This technique could be adapted for identifying T-PCD microflora in the alimentary tracts of other species.

 

Summarised by Joanna Horsfall

 

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