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Digestion, nutrition & metabolism

Detection of Helicobacter species in the gastrointestinal tract of ringtail possum and koala: Possible influence of diet, on the gut microbiota

Coldham, T, Rose, K, O’Rourke, J, Neilan, BA, Dalton, H, Lee, A & Mitchell, H 2013, Veterinary Microbiology, vol. 166, pp. 429-437.

Cultures from the liver and distinct regions of the gastrointestinal tract (GIT) revealed no Helicobacter species to be present in studied koalas. Deoxyribonucleic acid (DNA) extraction from stomach mucus scrapings and homogenised livers enabled gene sequencing of the 16S rRNA gene which was later identified to be of Helicobacter species. Examination of liver and intestine sections using histopathological methods further showed that the presence of Helicobacter was not related to infection.

  The detection of Helicobacter species was attempted using three techniques: polymerase chain reaction (PCR), culture and microscopy. Previous studies have shown that microorganisms associated with the mucosa are motile and may vary in composition at different GIT locations. To address this inconsistency, the authors of the present study collected tissue samples at the rectum, colon, caecum, liver, stomach as well as the ileum. Microscopy was performed following the bacterial culturing of these tissues, and no bacteria with a fusiform, spiral or thin shape suggestive of Helicobacter species were detected in any of the koalas. These morphological shapes of Helicobacter species had previously been reported in the lower bowel of other marsupials like the brushtail possum. The isolates were determined not to be of Helicobacter origin because of their abnormal colony appearance, morphology and the results of the Helicobacter-specific PCR. Using the nested PCR method, however, Helicobacter DNA was detected in the livers and stomachs of the koalas. Confirmation of these results was performed by sequencing the 16S rRNA gene from DNA extracted from the stomach and liver. Sequence comparison with a Genbank database produced a 99% similarity of liver-extracted DNA with Helicobacter bilis and 99% similarity of stomach-extracted DNA with Helicobacter felis. In one koala, Helicobacter DNA was also detected in the ileum and colon. Significant histopathological changes associated with Helicobacter species in the GIT, stomach or liver were not observed in the koalas.

  Helicobacter is a genus of bacteria that encompasses approximately 35 species. It has been postulated that rates of higher cultivation of Helicobacter spp. in other marsupials, such as the ringtail possum, may suggest that the limited diet of eucalypt leaves in koalas may hinder conditions that would favour Helicobacter colonisation in the lower bowel. Koalas were found to carry more small particles in the caecum and proximal colon than in the stomach or distal colon, and this is attributed to the selective retention of these particles for the fermentation of microorganisms. The authors of the present study reason that the conditions of the koala’s caecum and colon may therefore not be suited for colonization by Helicobacter spp.

  The findings of this article contribute to growing evidence of the ability of Helicobacter species to colonise the GIT of marsupials. Future research on Helicobacter species presence in omnivores and carnivores may provide additional insights into its natural niche and further our ecological understanding of the bacterial species.

 

Summarised by Alexander Murdoch

 

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