80 million bacteria sealed with a kiss

As many as 80 million bacteria are transferred during a 10 second kiss, according to research published in the open access journal Microbiome. The study also found that partners who kiss each other at least nine times a day share similar communities of oral bacteria.

The ecosystem of more than 100 trillion microorganisms that live in our bodies – the microbiome – is essential for the digestion of food, synthesizing nutrients, and preventing disease. It is shaped by genetics, diet, and age, but also the individuals with whom we interact. With the mouth playing host to more than 700 varieties of bacteria, the oral microbiota also appear to be influenced by those closest to us.

Researchers from Micropia and TNO in the Netherlands studied 21 couples, asking them to fill out questionnaires on their kissing behaviour including their average intimate kiss frequency. They then took swab samples to investigate the composition of their oral microbiota on the tongue and in their saliva.

The results showed that when couples intimately kiss at relatively high frequencies their salivary microbiota become similar. On average it was found that at least nine intimate kisses per day led to couples having significantly shared salivary microbiota.

Lead author Remco Kort, from TNO's Microbiology and Systems Biology department and adviser to the Micropia museum of microbes, said: “Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behavior unique to humans and is common in over 90% of known cultures.

Interestingly, the current explanations for the function of intimate kissing in humans include an important role for the microbiota present in the oral cavity, although to our knowledge, the exact effects of intimate kissing on the oral microbiota have never been studied. We wanted to find out the extent to which partners share their oral microbiota, and it turns out, the more a couple kiss, the more similar they are.”

In a controlled kissing experiment to quantify the transfer of bacteria, a member of each of the couples had a probiotic drink containing specific varieties of bacteria including Lactobacillus and Bifidobacteria. After an intimate kiss, the researchers found that the quantity of probiotic bacteria in the receiver's saliva rose threefold, and calculated that in total 80 million bacteria would have been transferred during a 10 second kiss.

The study also suggests an important role for other mechanisms that select oral microbiota, resulting from a shared lifestyle, dietary and personal care habits, and this is especially the case for microbiota on the tongue. The researchers found that while tongue microbiota were more similar among partners than unrelated individuals, their similarity did not change with more frequent kissing, in contrast to the findings on the saliva microbiota.

Commenting on the kissing questionnaire results, the researchers say that an interesting but separate finding was that 74% of the men reported higher intimate kiss frequencies than the women of the same couple. This resulted in a reported average of ten kisses per day from the males, twice that of the female reported average of five per day.

To calculate the number of bacteria transferred in a kiss, the authors relied on average transfer values and a number of assumptions related to bacterial transfer, the kiss contact surface, and the value for average saliva volume.

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Notes to editor:

1. Research article

Shaping the oral microbiota through intimate kissing
Remco Kort, Martien Caspers, Astrid van de Graaf, Wim van Egmond, Bart Keijser and Guus Roeselers
Microbiome 2014, 2:41

After embargo, article available at journal website here: http://www.microbiomejournal.com/content/2/1/41

Please name the journal in any story you write. If you are writing for the web, please link to the article. All articles are available free of charge, according to BioMed Central's open access policy.

2. The central purpose of the open access journal Microbiome is to unite investigators conducting microbiome research in environmental, agricultural, and biomedical arenas.

Topics broadly addressing the study of microbial communities, such as, microbial surveys, bioinformatics, meta-omics approaches and community/host interaction modeling will be considered for publication. Through this collection of literature Microbiome hopes to integrate researchers with common scientific objectives across a broad cross-section of sub-disciplines within microbial ecology.

3. BioMed Central is an STM (Science, Technology and Medicine) publisher which has pioneered the open access publishing model. All peer-reviewed research articles published by BioMed Central are made immediately and freely accessible online, and are licensed to allow redistribution and reuse. BioMed Central is part of Springer Science+Business Media, a leading global publisher in the STM sector. http://www.biomedcentral.com

4. Professor Remco Kort's work represents a collaboration between Micropia, the world's first museum of microbes in Amsterdam and the Netherlands Organisation for Applied Scientific Research (TNO) and scientifically underpins the kiss-o-meter in Micropia. Micropia shows the invisible, introducing a wide public to the world of the microbe. It provides information about current issues, on the importance of microbes to man and nature, and on the opportunities they offer us. Micropia's museum premises, its activities and website connect scientists, politicians, the business community, students, school pupils, journalists and everyone who is interested.

Micropia's kiss-o-meter allows people to discover just how many and what type of microbes they exchange during an intimate kiss. The mouth alone is home to 700 different kinds of bacteria. Despite being invisible, they are among the most successful life forms on earth and Micropia puts them on show. Professor Kort's kissing research exemplifies how Micropia makes the world of micro-organisms accessible to the general public. Remco Kort is a microbiologist and principal scientist at TNO and is Professor of Microbial Genomics at Amsterdam's VU University. He has been an adviser to Micropia for eight years.

For more information on Micropia, please contact Janna Laeven. Telephone: +31 (0) 20 52 33 515 / +31 (0) 6 13 98 70 41. E-mail: j.laeven@artis.nl. Or go to http://www.micropia.nl

5. About TNO

The 3000 TNO professionals put their knowledge and experience to work in creating smart solutions to complex issues. These innovations help to sustainably strengthen industrial competitiveness and social wellbeing. TNO is partnered by some 3000 companies and organizations, including SMEs, in the Netherlands and around the world. On the topic of Healthy Living we initiate technological and societal innovation for healthy living and a dynamic society. For more information about TNO and the five societal themes that are the focus of their work, go to http://www.tno.nl