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Microflora of the pouch of the koala (Phascolarctos cinereus)

Osawa, R, Blanshard, WH & O’Callaghan, P 1992, Journal of Wildlife Diseases, vol. 28, no. 2, pp. 276-280.

The pouches of female koalas are resistant to microbial colonisation, with a majority of pouch swabs revealing no microbial growth. Of 17 female koalas, only four (24%) were observed to have bacterial or yeast growths in the pouch.

  The pouches examined were of 17 females in a captive population at Lone Pine Koala Sanctuary. While the authors hypothesised that the warm, humid pouch environment would encourage microbial growth, especially for mothers with pouch young given the increased possibility of introducing novel bacteria with the entrance of the young into the pouch, the opposite was found to be true. From the pouches of four females with no dependent young, seven females supporting pouch young, and two females with back young, no microbial growth was detected. Of the remaining four koalas in which microbial pouch growths were observed, three had been supporting pouch young during the current breeding season which had all died before sampling occurred. In these females, the most commonly detected microorganisms were Pseudomonas aeruginosa, Serratia marcescens and Enterococcus faecalis. Acinetobacer lwoffi, Klebsiella pneumoniae and Streptococcus bovis were detected in low abundance in only single animals, and an unidentified yeast dominated the pouch of one of the females. It is not clear whether these infections were the cause or the result of the mortalities of the three females’ pouch young.

  In contrast to the authors’ predictions, the findings of this study support the conclusion that the pouch of the koala is a hostile environment that is resistant to microbial colonisation as no microflora were isolated from the majority of females sampled. Given the potential link observed here between infection and pouch young mortality, the hostility of the pouch epithelium to microbial colonisation may afford additional protection to the growing joey.

  The findings of this study enhance our understanding of the mechanisms that support or hinder the survival of pouch young, as well as of the reproductive biology of the koala more broadly.


Summarised by Joanna Horsfall


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