The oral microbiome of children, and its relation to dental caries

The oral microbiome is a popular area of exploration because bacteria are a prominent part of dental health, and because it is one of the most heavily colonized and easily accessible niches in the body. Many studies have been discussed on this blog concerning adult oral microbiomes, and its relations to bodily issues such as cystic fibrosis and periodontitis. It is also very useful to investigate children and the ways that their bacterial communities first inhabit and develop. A study done in Sweden at the Umeå University, and published by Plos One, takes a look at the maturation of the oral microbiome from infants at 3 months old to children at 3 years old.

The Swedish researchers performed a longitudinal study that followed children from 3 months to 3 years of age, looking for microbial characteristics of children with dental caries (i.e. cavities) compared to those without. There were 207 original participating 3 month olds that were consented by their parents to be in the study. The parents provided information on mode of feeding, mode of delivery, use of antibiotics or probiotics, health issues like allergies, and presence of teeth. At 3 months and later at 3 years samples were taken from the buccal mucosa, tongue, and alveolar ridges. Teeth were also scraped for plaque and saliva was collected. Of the original 207 participants, 155 returned for sampling at 3 years of age, and 13 of those children had dental caries.

After sequencing the bacterial DNA samples, it was found that Escherichia coli, Staphylococcus epidermidis, and various Pseudomonas species were significantly more prevalent in 3 month olds. However, there were 23 genera that were more significantly prevalent at 3 years of age than at 3 months.

By comparing the children with and without caries, the scientists were able to make several conclusions.  The researchers identified seven taxa that appear to be associated with healthy teeth.  On the other hand, Streptococcus mutans seemed to be more prevalent in the children with caries, than in those without caries. Additionally, the colonization of this species was most prevalent in girls. This is possibly because girls develop faster, so earlier tooth eruption allows for a longer time for the colonization of these bacteria.

The results of this study show us that during the first three years of life, species richness and diversity seems to increase significantly in the mouth. While there is an increase in the type of the bacteria, there are also some taxa that are lost with age. The researchers also concluded that the oral microbial composition of the mouth at 3 months does not appear related to the development of dental caries. With this information, it might be smart to perform a related study that collects oral microbiome samples in children within the time frame of 3 months to 3 years, because it could show a clearer picture of the changes that take place in bacterial composition.

The oral microbiome of the medieval man

Plaque that forms on teeth, also called calculus, can be preserved for a very long time, and traps all types of biomolecules and bacteria that are found in our mouths. An article published by Nature Genetics explores a study conducted to observe the oral microbiome on calculi of ancient human teeth and its differences from the oral microbiome that exists today. In this study, the ancient calculi showed the historical importance of gene transfer in the microbiome, which has been, and still is a rich consortium of bacteria that readily and rapidly exchange gene. 

The researchers studied the teeth of four adult human skeletons from the medieval city of Dalheim, Germany, who showed signs of mild to severe periodontal disease, as well as the current teeth of nine people. Interestingly, the same bacteria, proteins, and pathogens were identified in both the ancient and modern calculus, despite the differences in oral hygiene and diet between each time period. Researchers also found evidence of antibiotic resistance genes, like efflux pumps, in many members of the ancient plaque.  This means that horizontal gene transfer was clearly occurring between members of the oral microbiome, and the genes for some forms of antibiotic resistance have ancient roots.  However, other genetic adaptations for antibiotic resistance against modern drugs were not identified, even those that are ubiquitous in the oral microbiome today.  This should be no surprise, as modern antibiotics were not in use in the Middle Ages.

Medieval dental calculi, and fecal samples for that matter, give us a peak at what the ancient microbiome looked like.  By studying it, we can learn how the human oral microbiome has adapted over time in response to changes in human behavior, diets, hygiene, and antibiotic use.