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Two teeth from a man who lived around 4,000 years ago were found to contain an abundance of bacteria that mainly cause tooth decay and gum disease. The rare discovery could help scientists further understand how the prevalence of cavities today is a result of changes in the human diet.
The teeth were revealed during two excavations from 1993 and 1996, among a number of human teeth and other remains found within limestone caves in County Limerick in Ireland. The two moles sampled, dating between 2280 and 2140 BC, were from the same person who lived during the Bronze Age, according to the paper published Wednesday in the journal Molecular Biology and Evolution.
One tooth had a surprising abundance of Streptococcus mutans (S. mutans), an oral bacteria that causes cavities. The bacteria is rare in the ancient genomic record, likely because it doesn’t preserve well due to its acid-producing nature that causes decay and DNA degradation within teeth, said Lara Cassidy, senior author of the paper and assistant professor in the Department. genetics at Trinity College, Dublin.
Researchers also believe that the bacteria were less commonly found in ancient teeth because there was less refined sugar and less processed foods in the human diet than is consumed today, Cassidy said. A significant dietary change was seen with the onset of agriculture about 10,000 years ago, but major changes have been seen in the last few years with the cultivation of sugar, she said.
Link between dietary changes and tooth decay
It’s unclear why the bacteria on the newly discovered tooth were so well preserved, but Cassidy said the cave’s cool, dry conditions are likely factors.
Although cavities have been observed on other ancient tooth finds, S. mutans has only been found in very low amounts in a handful of remains, such as an older, Neolithic tooth from southwestern France (dating between 3400 and 2900 BC) or a chewing field . from the Scandinavian Mesolithic (dating between 9890 and 9540 BC). Cavity impressions from other ancient teeth become more frequent after the adoption of cereal agriculture, the farming of grains such as wheat and barley, according to the paper.
By analyzing the bacteria found on Bronze Age teeth and comparing it to modern samples, the researchers discovered that the ancient S. mutans evolutionary tree was more complex than first thought — and they found the characteristics of ancient bacteria, such as virulence (ability to cause). damage), have evolved along with changes in the human diet, including the popularity of sugar and grains, Cassidy said.
“In the last few hundred years there has been an insane amount of change (in the human diet), so understanding in particular how it has affected the microbiome (the microorganisms, such as bacteria, that naturally live on and within the human body), not only on the Oral microbiome, the gut microbiome as well, may help us to understand why certain diseases have become so common in Western populations or in western populations for a few last century,” she said.
Bronze Age oral health
No signs of tooth decay were found on the Bronze Age teeth, but if the adult male they were with had lived a little longer, the abundance of bacteria suggests he would have developed cavities early on, he said. Cassidy.
Both teeth also contained DNA evidence of Tannerella forsythia (T. forsythia), a bacteria associated with gum disease that is found more frequently in the ancient genome record. But the researchers found two distinct strains of bacteria within the teeth – today, only one strain of bacteria is commonly seen, suggesting that ancient microbiomes were much more diverse than modern microbiomes. modern. The loss of biodiversity is a matter of concern because it can have a negative impact on human health, according to a news release from Trinity College, Dublin.
Several other teeth found inside the cave showed signs of tooth decay, but it is not known whether those remains were the same person or other members of the community as they were found undivided, separated from other skeletal remains, Cassidy said. . “Other teeth from his mouth may have had cavities, or other members of his community may have had dental disease.”
Analysis of ancient S. mutants suggests that the bacteria have become more prevalent in recent centuries due to sugar consumption, which created a favorable habitat for the species inside the human mouth, Cassidy added. By understanding the evolution of modern cavity-causing bacteria, it also helps scientists understand how a change in diet can affect oral health today, she said.
The analysis of the ancient S. mutans compared to the modern S. mutans revealed “a major change over the past few centuries related to increased sugar consumption” and supports previous research that found higher rates of cavity tar after refined sugar became widespread. available in the 19th century, said Louise Humphrey, head of research at the Center for Human Evolution Research at the Natural History Museum, London, who was not involved in the study.
“The oral microbiome has implications for many areas of human health and disease. … ancient teeth can help us understand how the human oral microbiota (the realm of microorganisms) has evolved over time and how these changes have affected human health in the past around and today,” Humphrey said in an email.
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