Ten second kiss can transfer 80 million bacteria

London: Couples, take note! As many as 80 million bacteria are transferred during 10 seconds of kissing, according to a new study that found partners who kiss at least nine times a day share similar communities of oral bacteria.

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 museum and the Netherlands Organisation for Applied Scientific Research (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.

"Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behaviour unique to humans and is common in over 90 per cent of known cultures," lead author Remco Kort, from TNO's Microbiology and Systems Biology department, said.

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 Bifido bacteria.

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. The research was published in the journal Microbiome.