Rare ancient bacteria found on Bronze Age teeth reveal the impact a major dietary change had on human health

By | March 27, 2024

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Two teeth from a man who lived about 4,000 years ago have been discovered to contain an abundance of bacteria that mainly cause tooth decay and gum disease. The rare find could help scientists better understand how changes in the human diet have led to the prevalence of cavities today.

The teeth were discovered during two excavations in 1993 and 1996 and were among several human teeth and other remains found in a limestone cave in County Limerick in Ireland. The two sampled molars, dating between 2280 and 2140 BC, were both from the same individual who lived during the Bronze Age, according to the paper published Wednesday in the journal Molecular Biology and Evolution.

One tooth contained a surprising abundance of Streptococcus mutans (S. mutans), an oral bacteria that causes cavities. The bacterium is rare in the ancient genomic record, likely because it is not well preserved due to its acid-producing nature that causes decay and DNA breakdown in teeth, said Lara Cassidy, senior author of the paper and assistant professor in the department of dentistry. genetics at Trinity College Dublin.

Researchers also believe the bacteria is not as common in old teeth because the human diet contained less refined sugar and fewer processed foods than is consumed today, Cassidy said. With the start of agriculture about 10,000 years ago, a significant change in diet was observed, but major changes have occurred in recent hundreds of years with the popularization of sugar, she added.

A link between dietary changes and tooth decay

It’s unclear why the bacteria on the newly discovered tooth were extremely well preserved, but Cassidy said the cool and dry conditions in the cave were likely factors.

Although cavities have been observed in other ancient tooth finds, S. mutans has only been discovered in very small quantities in a handful of remains, such as an older, Neolithic tooth from southwestern France (dating between 3400 and 2900 BC) or a chewed pitch. from the Scandinavian Mesolithic (dating between 9890 and 9540 BC). Observations of cavities of other ancient teeth have become more common after the adoption of grain agriculture, the farming of grains such as wheat and barley, the paper said.

By analyzing the bacteria on Bronze Age teeth and comparing them to modern samples, researchers discovered that the ancient evolutionary tree of S. mutans was more complex than previously thought – and had discovered the ancient bacteria’s properties, such as virulence (the ability to cause harm), which has developed alongside changes in the human diet, including the popularization of sugar and grains, Cassidy said.

“There has been a tremendous amount of change (in the human diet) over the past few hundred years, so especially understanding how that has affected the microbiome (the microorganisms, such as bacteria, that naturally live on and in the human body), and not just the The oral microbiome, and also the gut microbiome, could help us understand a little bit why certain diseases have become so prevalent in Western populations or Westernized populations in recent centuries,” she added.

Oral health of the Bronze Age

No signs of tooth decay were found on the Bronze Age teeth, but if the adult male they belonged to had lived a little longer, the abundance of bacteria present suggests he would have quickly developed cavities, Cassidy said.

The two teeth also contained DNA evidence of Tannerella forsythia (T. forsythia), a bacterium implicated in gum disease and more common in the ancient genome record. But the researchers had found two different strains of bacteria in the teeth. Today, only one strain of bacteria is found, implying that ancient microbiomes were much more diverse than modern microbiomes. The loss of biodiversity is worrying because it can have negative impacts on human health, according to a press release from Trinity College Dublin.

The several other teeth found in the cave showed signs of tooth decay, but it is unknown whether these remains belong to the same individual or to other members of the community as they were found disarticulated, separated from other skeletal remains, Cassidy said . “It is possible that other teeth from his mouth had cavities, or that other members of his community suffered from dental disease.”

Analysis of ancient S. mutans suggests that the bacterium has become increasingly common in recent centuries due to sugar consumption, creating a favorable habitat for the species in the human mouth, Cassidy added. Understanding the lineages of the modern bacteria that cause cavities will help scientists further understand how dietary changes today can affect oral health, she said.

The analysis of ancient S. mutans compared to modern S. mutans “revealed a major change over the past few hundred years related to increased sugar consumption” and supports previous research that had revealed higher rates of cavities after refined sugar became widespread. available in the 19th century, said Louise Humphrey, research director at the Center for Human Evolution Research at the Natural History Museum in London, who was not involved in the study.

“The oral microbiome has implications for many areas of human health and disease. …old teeth can help us understand how the human oral microbiota (range of microorganisms) has evolved over time and the impact of these changes on human health in the past and today,” Humphrey said in an email -mail.

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