Characterisation of and immunity to the aerobic bacteria found in the pouch of the brushtail possum Trichosurus vulpecula

The bacterial composition of the brustail possum (Trichosurus vulpecula) pouch was characterized throughout the reproductive cycle using brushtails from an Australian captive breeding colony (45 swabs) and a wild population in New Zealand (26 swabs). Gram-positive coccal species predominate throughout the reproductive cycle. Enteric Gram-negative rods, particularly Escherichia coli, were most prevalent when a pouch young was present and was most likely the result of faecal contamination from the pouch young. As culturing is only able to detect a proportion of bacteria present in a particular environment, molecular 16S rDNA sequencing was carried out on DNA extracted from a pouch wash of a female carrying a pouch young to gain a more accurate assessment of the pouch microflora. This approach identified approximately five times the number of bacterial species when compared to culture results. The majority detected were Gram negative rods or most closely related to Gram-negative rods species. Brushtails are immunologically immature at birth yet survive in a pouch colonised with potentially pathogenic bacteria. A haemagglutination assay was used to determine whether antibodies to a frequently isolated bacterium (Klebsiella pneumoniae) were transferred via milk from mother to pouch young. IgG antibodies were detected in maternal serum, milk and pouch young serum. In young over 70 days, antibody fitres were significantly higher than those found in maternal serum, suggesting that the young is capable of producing adult type antibodies to pouch bacteria at this time.