Oxalate-degrading bacteria, including Oxalobacter formigenes, colonise the gastrointestinal tract of healthy koalas (Phascolarctos cinereus) and those with oxalate nephrosis.

BACKGROUND: Koalas in the Mount Lofty Ranges, South Australia, have a high prevalence of oxalate nephrosis, or calcium oxalate kidney crystals. Gastrointestinal tract oxalate-degrading bacteria, particularly Oxalobacter formigenes, have been identified in other animal species and humans, and their absence or low abundance is postulated to increase the risk of renal oxalate diseases. This study aimed to identify oxalate-degrading bacteria in the gastrointestinal tract of koalas and determine their association with oxalate nephrosis. METHODS: Caecal and faecal samples were collected at necropsy from 22 Mount Lofty Ranges koalas that had been euthanased on welfare grounds, with 8 koalas found to have oxalate nephrosis by renal histopathology. Samples were analysed by PCR for the oxc gene, which encodes oxalyl-CoA decarboxylase, and also by Illumina sequencing of the V3-V4 region of the bacterial 16S rRNA gene. RESULTS: The oxc gene was detected in 100% of koala samples, regardless of oxalate nephrosis status. Oxalobacter formigenes was detected in all but one faecal sample, with no difference in abundance between koalas affected and unaffected by oxalate nephrosis. Other species of known oxalate-degrading bacteria were infrequently detected. CONCLUSION: This is the first study to identify Oxalobacter and other oxalate-degrading bacterial species in koalas, but an association with oxalate nephrosis and absence or low abundance of Oxalobacter was not found. This suggests other mechanisms underlie the risk of oxalate nephrosis in koalas.