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Characterisation of gram-negative anaerobic strains, isolated from koala faeces, which exhibit satellite growth and pleomorphism

Osawa, RO, Fujusawa, T & Mitsuoka, T 1992, Systematic and Applied Microbiology, vol. 15, no. 1, pp. 628-635.

As part of a series of studies investigating the characteristics of koala faecal microflora, three strains of anaerobic gram-negative bacteria which demonstrated satellitism around colonies of Escherichia coli are described here.

  Fresh faecal samples were collected from three healthy koalas at Lone Pine Koala Sanctuary, Brisbane. Solutions of diluted faecal matter from each of the three koalas were plated onto Wilkins-Chalgren Anaerobe (WCA) agar with 5% defibrinated horse blood, which were then incubated anaerobically for five days at 37OC. After this incubation period, small transparent colonies were observed growing around larger colonies of E. coli. This phenomenon is termed ‘satellitism’ and occurs when a bacterial species grows more successfully when it is immediately adjacent to a colony of an unrelated species. Three strains from these satellite colonies were subcultured onto WCA plate media and their morphologies examined. The strains were found to be anaerobic, gram-negative, highly pleomorphic, bile resistant, and asaccharolytic (incapable of breaking down carbohydrates). The growth of the strains was accelerated by succinic acid and completely suppressed by fumaric acid. The production of succinic acid by E. coli may be responsible for the observed satellitism of these strains. These anaerobic koala strains may, therefore, demonstrate similar satellite growth around colonies of other bacteria that produce succinic acid.

  To build upon the findings of this study, the authors recommend further examination of a broader range of anaerobic strains to more clearly define the distinctive morphological, physiological and biochemical characteristics of the anaerobic koala strains studied here.

 

Summarised by Joanna Horsfall

 

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