Up to 80 million bacteria can be transferred between couples during just one 10-second kiss, researchers in the Netherlands have found, and couples who kiss up to nine times a day end up with very similar communities of oral bacteria because of it.

There's an ecosystem of more than 100 trillion microorganisms living in and on our bodies. We barely even notice they're there, but they're helping to digest our food, break down nutrients, and protect us from disease. Without them, we wouldn't survive a day. According to NPR, US-based biologist Jeffrey Gordon from Washington University once said:

"We think that there are 10 times more microbial cells on and in our bodies than there are human cells. That means that we're 90 percent microbial and 10 percent human. There's also an estimated 100 times more microbial genes than the genes in our human genome. So we're really a compendium [and] an amalgamation of human and microbial parts."

So just like the Portuguese man-o'-war - which is a collection of many different simple organisms that have come together to form a very powerful, very functional, collective 'being' - humans can also be thought of as a colonial organism. In our mouths alone, we've got 700 varieties of bacteria, and while these are influenced by our genetics, diet and age, new research has found that they're also influenced by the people closest to us.

Researchers from the Netherlands Organisation for Applied Scientific Research (TNO) worked with 21 couples, asking them to complete questionnaires about how often they kiss each day and how long each kiss usually lasts. The team then took a swap samples from instead their mouths to identify what oral microbiota they had living on their tongues and in their saliva.

Publishing their results in the journal Microbiome, the team discovered that couples that kissed for a long time often - at least nine times daily - had ended up with very similar microbial communities in their mouths. 

The team also counted how many microbes were passed between kissing couples by getting one of them to consume a probiotic drink containing known varieties of bacteria such as Lactobacillus and Bifidobacteria. They were asked to kiss in a controlled environment, and the researchers counted how many of these specific bacteria were passed on to the other person. They found that, on average, some 80 million bacteria will be transferred during a 10-second kiss.

"Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behaviour unique to humans and is common in over 90 percent of known cultures," lead researcher Remco Kort from TNO's Microbiology and Systems Biology department and the Netherlands' Micropia Museum of Microbes, said in a press release. "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."

Now there's a bunch of great new science to break the ice with on a first date. You're welcome.

Source: EurekAlert, NPR