The diversity of the oral microbiome 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 'Saca la Lengua' scientific team of the Centre for Genomic Regulation (CRG), led by Dr. Toni Gabaldón, with the support of the "la Caixa" Foundation.
The study of 1,648 people, aged between 7 and 85 years, spread throughout Spain, reveals the existence of a parabolic trend that results in three distinct stages in the composition of microorganisms residing in the mouth.
According to the authors of the study, adolescents have a highly biodiverse oral microbiome that varies greatly from person to person, which may be related to hormonal and habit changes during this phase. Middle-aged people have a lower biodiversity and also a more homogeneous composition between individuals, representing a stage of high stability. From the age of 60 onwards, biodiversity and differences between individuals increase again and very considerably.
The authors of the study realised that the high diversity of the oral microbiome in older people was the cause of the establishment of rare opportunistic species, almost all of which are linked to oral diseases such as periodontitis. The authors postulate that the difference between middle and old age may be due to differences in the immune system, which weakens with age and makes the oral cavity more susceptible to colonisation by opportunistic species that would normally be rejected.
In order to understand the environmental and/or lifestyle characteristics that influence the oral microbiome, study participants completed a questionnaire examining 80 different aspects of lifestyle, diet, hygiene and health.
Factors associated with major changes in the oral microbiome are linked to chronic diseases such as cystic fibrosis or syndromes such as Down's syndrome, followed by lifestyle factors such as smoking. Each of these factors changed the microbiome in a particular way, resulting in a specific signal. Coeliac disease, hypertension and antibiotic use also played a role, albeit to a lesser extent.
The impact of social and family relationships also influences 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 than between two people from different families. The association even exists between members of the same school class, a finding that leads the authors to postulate 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 accelerate the development of techniques that use saliva to report on the health status of individuals.
"Oral health is connected to the whole 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 to interpret the language of the oral microbiome in such a way that, one day, saliva sampling may be as routine as blood or urine tests," says ICREA Research Professor Toni Gabaldón, scientific leader of the 'Saca la Lengua' project, and currently group leader 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 syndromes such as Down's syndrome have a different and characteristic oral microbiome. The differences found are related to specific problems in these people. For example, a higher presence of periodontitis-associated species in people with Down's syndrome, and a higher presence of opportunistic respiratory tract pathogens in people with cystic fibrosis. A better understanding of the oral microbiome in these individuals paves the way for targeted treatments to reduce these risks, which could consist of pre- or probiotics specifically designed for this purpose.
'Saca la Lengua' is a citizen science project promoted by the Centre for Genomic Regulation and the "la Caixa" Foundation that 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 relationship of the oral microbiome with environmental and/or lifestyle characteristics among adolescents.
Following the success of the first project, the second edition of 'Stick Out Your Tongue' was launched in 2017 with the aim of expanding the first portrait of the oral microbiome with data from other age groups or patients with certain diseases such as celiac disease, cystic fibrosis, or syndromes such as Down syndrome.
The 'Saca la Lengua' scientific team visited more than 30 schools and civic centres in several cities in Spain. The team set up a van with the necessary equipment for the initial processing of the saliva samples, travelling more than 7,000 kilometres between Catalonia, the Balearic Islands, the Valencian Community, Murcia, Andalusia, Madrid, Galicia, the Basque Country and Aragon.
"This was conceived from the outset as a participatory project, in which citizens could contribute not only with a saliva sample, but also with the questions to be explored and the prioritisation of the data to be analysed," says Dr Elisabetta Broglio, Citizen Science Coordinator at the CRG. "Between patients' associations, bars, museums, schools, civic centres and senior citizens' classrooms, everyone pitched in to be part of the study. Without this massive participation it would have been impossible to achieve results with this level of resolution."
"The first edition of 'Saca la Lengua' was a resounding success. That's why we launched a second edition, to further advance our knowledge of the microbiome. When we conceived the idea we could not have predicted the success of the project both on a citizen science and 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 has the support and contribution of the companies Illumina, Eppendorf, miniPCR, and ThermoFisher Scientific. The Genomics and Bioinformatics services of the CRG, key in the development of the project, are co-funded by the European Union through the European Regional Development Funds (ERDF).