The devastating event known as the "Black Death" or "Second Plague Pandemic" that occurred in the mid-14th century resulted in the death of 30-60% of the European population and greatly changed the historical trajectory of Europe. Recent research by a team from Penn State and the University of Adelaide suggests that the pandemic may have inadvertently affected the human oral microbiome. Post-plague changes in diet and hygiene may have led to shifts in the oral microbiome that contribute to the development of chronic diseases in modern humans.
"The modern microbiome is associated with a variety of chronic diseases, including obesity, cardiovascular disease and poor mental health," said Laura Weyrich, associate professor of anthropology at Penn State. "Uncovering the origins of these microbial communities may help understand and control these diseases."
Challenges facing microbiome research
Dietary changes are thought to influence the evolution of the oral microbiome over time; however, few studies have directly examined the history of the human oral microbiome within a single population, Weirich said. Weirich points out that some studies have replaced pre-industrial microbiomes with microbiomes living among indigenous peoples who lived traditional subsistence lifestyles. However, she says this strategy is wrong because the microbes of modern non-industrialized populations may not accurately reflect the microbes of the ancestors of industrialized populations.
Additionally, she said, "This study places unnecessary responsibility and liability on Indigenous communities to participate in microbiome research, the benefits of which may not directly serve Indigenous peoples."
A more accurate and ethical approach would be to directly study the oral microbiome preserved in the calcified dental plaque (i.e., dental calculus) of the ancestors of industrialized peoples, with the consent and cooperation of the deceased and stakeholders. In the largest study of ancient dental calculus to date, Weyrich and her colleagues collected dental material from 235 people buried at 27 archaeological sites in England and Scotland from 2200 BC to 1853 AD.
The findings were recently published in the journal Nature Microbiology.
The researchers processed the samples in an ultra-sterile ancient DNA laboratory to minimize contamination. They identified 954 microbial species and determined that they belonged to two distinct bacterial communities - one dominated by the genus Streptococcus - which is common in the oral microbial communities of modern industrialized country populations; and the other dominated by the genus Methanobacterium - which is currently considered extinct in healthy industrialized country populations.
In exploring the origins of these two communities, the team found that nearly 11% of the total variation in microbiome species composition could be explained by temporal changes, including the arrival of the second plague pandemic. But how did the second plague pandemic lead to changes in the oral microbiota?
Impact of the second plague pandemic on the oral microbiome
"We know that survivors of the second plague pandemic had higher incomes and were able to afford higher-calorie foods," Weirich said. "The pandemic may have triggered changes in people's diets that affected the composition of their oral microbiomes."
The research team used a new approach to investigate whether changes in diet affect the emergence of Streptococcus species and the extinction of Methanobacterium species. They listed possible diet-related functional differences between the two groups of bacteria, such as those related to high- or low-dietary fiber digestion, carbohydrate metabolism, and lactose (a sugar in milk) metabolism.
The researchers found that more functional traits in the Streptococcus-dominated bacterial group were significantly linked to low-fiber, high-carbohydrate diets and dairy consumption, all of which are hallmarks of modern diets. In contrast, the Methanobacterium-dominated group lacked traits associated with dairy and sugar consumption that characterize some ancient human diets.
The connection between the microbiome and disease
The team further determined that Streptococcus bacteria are associated with the presence of periodontal disease, which is characterized by infection and inflammation of the gums and bone surrounding the teeth. When the disease worsens, bacteria can enter the bloodstream through the gum tissue and can cause respiratory disease, rheumatoid arthritis, coronary artery disease and blood sugar problems in people with diabetes. The Methanobacterium group is associated with bone lesions.
"Our study shows that the modern oral microbiome may reflect past dietary changes resulting from the second plague pandemic," Weirich said. "Importantly, this work contributes to our understanding of modern chronic non-communicable diseases."
Compiled from /ScitechDaily