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 journalMicrobiome. 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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