Citizen science reveals first comprehensive snapshot of the oral microbiome

Oral microbiome diversity changes significantly with age, according to the results of a new study published today in the scientific journal npj Biofilms and Microbiomes, developed by the scientific team of 'Saca la Lengua' at the Centre for Genomic Regulation (CRG) and directed by Dr. Toni Gabaldón with the support of the ”la Caixa” Foundation.

The study of 1,648 people between 7 and 85 years of age located all over Spain, reveals a parabolic trend that results in three distinct stages for the composition of microorganisms living in the mouth.

According to the authors of the study, teenagers have a highly biodiverse oral microbiome that varies greatly between individuals, which may be explained by hormonal and behavioural changes. Middle-aged people had lower biodiversity as well as a generally homogeneous composition between individuals, representing a stage of high stability. From the age of 60, biodiversity and the differences between individuals increased considerably.

Researchers believe that the high diversity of the oral microbiome in elderly people could be due to the establishment of rare opportunistic species, almost all of which are linked to oral diseases such as periodontitis. The authors hypothesise that the difference between middle and old ages may be due to differences in the immune system, which weakens with age, making the oral cavity more susceptible to colonization by opportunistic species that would otherwise normally not succeed.

In order to understand the environmental and/or lifestyle characteristics that influence the oral microbiome, study participants completed a questionnaire that examined 80 different aspects of lifestyle habits, diet, hygiene and health.

Factors associated with major changes in the oral microbiome were found to be linked to chronic diseases such as cystic fibrosis or conditions such as Down syndrome, followed by lifestyle habits such as smoking. Each of these factors changed the microbiome in a particular way, resulting in a specific signal. People with celiac disease, hypertension or those that used antibiotics also changed their oral microbiome in specific ways, although to a lesser extent than other factors.

The impact of social and family relationships also influenced the composition of the oral microbiome. Members of the same family – for example, parents and children, or two brothers or sisters – have a more similar microbiome compared to two people from different families. The association exists even among members of the same class in school, a finding that leads the authors to hypothesise that sharing the same environment, even for a few hours a day, can significantly affect the oral microbiome.

The results, which are the first study of changes in the diversity of the oral microbiome with age, could speed the development of techniques that use saliva to report on people's health status.

“Oral health is connected to the entire human body. For this reason, saliva contains a lot of useful information that can provide complementary information to other tests such as blood tests. The results of 'Saca la Lengua' provide a dictionary that helps interpret the language of the oral microbiome in such a way that, one day, using a saliva sample could be as routine as blood or urine tests,” says ICREA Research Professor Toni Gabaldón, Scientific Lead of the 'Saca la Lengua' project, and currently Group Leader with dual affiliation at the Institute for Research in Biomedicine (IRB Barcelona) and the Barcelona Supercomputing Center (BSC-CNS).

The study has found that people with chronic diseases such as cystic fibrosis or conditions such as Down syndrome have a different and specific oral microbiome related to the specific characteristics in people living with these conditions. The researchers found a higher presence of periodontitis-associated species in people with Down syndrome and a higher presence of opportunistic airway pathogens in people with cystic fibrosis. The knowledge paves the way for specific treatments that reduce risks associated to these findings, for example through the use of customised pre- or probiotics.

'Saca la Lengua' is a citizen science project promoted by the Centre for Genomic Regulation and the ”la Caixa” Foundation which aimed to discover the variety of microorganisms that live in our mouths. The first edition of the project was launched in 2015 with the aim of determining the link between the oral microbiome and environmental and/or lifestyle habits among teenagers.

The second edition of 'Saca la Lengua' was launched in 2017 with the aim of expanding the first snapshot of the oral microbiome with data from other age groups or from patients with certain diseases such as celiac disease, fibrosis cystic, or conditions such as Down syndrome.

The team visited more than 30 educational and community centres in various cities across Spain. The team equipped a van with the necessary equipment to process the saliva samples and travelled more than 7,000 kilometres between Barcelona, the Balearic Islands, the Valencian Community, Murcia, Andalusia, Madrid, Galicia, the Basque Country and Aragon.

"This was conceived from the beginning as a participatory project, in which citizens could contribute not only with their saliva but their minds, by telling us what questions we should explore and what data to analyse as a priority," says Dr. Elisabetta Broglio, Citizen Science Coordinator at the CRG. “We involved as many people as possible by visiting patient associations, bars, museums, schools, community centres and adult educational centres. Without the massive participation we got it would have been impossible to obtain the results at this scale.”

"The first edition of 'Saca la Lengua' was a resounding success. That's why we launched it a second time, to further advance our understanding of the microbiome. When we conceived the idea we could not predict the success of the project both at the citizen science level and at the scientific level. It is an example of an innovative project in which citizens have played an essential role”, says Dr. Luis Serrano, Director of the CRG.

The 'Saca la Lengua' project was supported by Illumina, Eppendorf, miniPCR, and ThermoFisher Scientific. The Genomics and Bioinformatics services of the CRG, key in the development of the project, are co-financed by the European Union through the European Regional Development Funds (ERDF).