of each donor. “An optimal donor has a poor diet and oral hygiene but good dental health. A good donor has a decent diet, regular oral hygiene, visits the dentist often and has good oral health. The suboptimal donor is someone who has had dental caries in the past but now has stable oral health.”1 A group of researchers at the Pennsylvania State University, led by Professor Laura Weyrich, is sequencing the DNA from bacteria in the oral microbiome samples that Dr. Zilm’s team collects. “We are mapping out the microbiome in these people’s mouths and that work is ongoing,” says Dr. Zilm. One of the PhD students on Dr. Zilm’s team developed the media in which they had isolated S. mutans from different donors. “We made a broth, we added sugar and measured the pH level after 30 minutes or so,” says Dr. Zilm. The experiment found a significant difference in the amount of acid made by different strains of S. mutans. “We’re going to do DNA sequencing so we can look at the specific genes in those bacteria to see why some produce more acid or others produce less,” says Dr. Zilm. Dr. Zilm and his team ran an experiment on rats to see if transplanting a microbiome from a super donor would protect teeth from caries. “There is already a well-documented rat caries model, where you feed rats a high sucrose diet,” says Dr. Zilm. During the experiment, two groups of rats received oral microbiome transplants, some from optimal donors and others from suboptimal donors. “Over 3 days, we initially washed the rats’ mouths out with chlorhexidine mouth rinse to suppress their existing microbiome and then introduced the transplant from the donors,” he says. The rats then ate a high sugar diet for 8 days. To make sure that the processes were safe, the team took blood serum to test for inflammatory markers and gut samples for histology. They also took swabs of the rats’ oral microbiomes and examined their jaws for caries. “We saw a statistically significant decrease in the caries in the rats that had the transplants, from both kinds of donors,” says Dr. Zilm. “We were a little bit surprised that it actually worked because it was such a new idea.” The team is still working with the data from the experiment to see if there was a complete shift to the introduced microbiome or if a hybrid microbiome resulted from the transplants. Dr. Zilm believes that oral microbiome transplants in humans could be an integral part of preventing caries in the future. “In a very early study, researchers just took a plaque sample from a donor dog and put it in the mouth of a recipient dog with periodontitis,” says Dr. Zilm. “We couldn’t do this in humans because it could potentially also transmit viruses and other pathogens.” Dr. Zilm’s team takes samples from human donors and then culture them in vitro in artificial saliva on 3D-printed hydroxypatite discs, which have enamel-like properties. In future, biofilm would be sequenced, to allow the researchers to know the biofilms’ exact constituents, then the biofilm would be stored in a biobank until it was needed for use.2 “At this point, it is still theoretical, but I can imagine that, in future, a microbiome transplant is something that would happen in dental clinics.” The next step for Dr. Zilm’s team is a clinical study in humans. “We are getting a lot of interest from different groups because a microbiome transplant is a different way of looking at solving oral diseases like caries and periodontal disease,” he says. References: 1. Nath S, Zilm PS, Jamieson L, Ketagoda DHK, Kapellas K, Weyrich L. Characterising healthy Australian oral microbiomes for ‘super donor’ selection. J Dent. 2024; Oct 24:105435. 2. Ketagoda DHK, Varga P, Fitzsimmons T, Moore N, Weyrich L, Zilm P. Development of an in vitro biofilm model of the human supra-gingival microbiome for oral microbiome transplantation. J Microbiol Methods. 2024; Aug 223:106961. Dr. Peter Zilm (2nd from left) and his research team at the University of Adelaide School of Dentistry. 17 Issue 1 | 2025 | News and Events
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