Shaping the oral microbiota by intimate kissing

Background: The variation of microbial communities associated with the human body can result from many contributing factors, including the human genetic makeup, diet, age, surroundings and sexual behavior. In this study we investigated the effect of intimate kissing on the oral microbiota from 42 individuals of 21 couples by self-administered questionnaires about past kissing behavior and evaluation of oral microbiota samples. We determined the composition of bacterial populations on the dorsal anterior part of the tongue and in saliva before and after an intimate kiss of 10 seconds. In addition, we quantified the number of bacteria exchanged during intimate kissing by the use of marker bacteria introduced through the intake of a probiotic yoghurt drink by one of the partners prior to a second intimate kiss. Results: Similarity indices of microbial communities show that on average partners have a more similar oral microbiota compared to unrelated individuals, with by far most pronounced similarity for communities associated with the tongue surface. An intimate kiss did not lead to a significant additional increase of the average similarity of the oral microbiota between partners. However, a clear positive correlation was observed between the similarity indices of the salivary microbiota of couples and self-reported kiss frequencies, and a negative correlation for the self-reported amount of time passed after the latest kiss. In our control experiments for bacterial transfer, we were able to identify probiotic Lactobacillus and Bifidobacterium marker bacteria in most kiss receivers, corresponding to an average total bacterial transfer of 80 million bacteria per intimate kiss of 10 seconds. Conclusions: This study indicates that a shared salivary microbiota requires a frequent and recent bacterial exchange and is therefore most pronounced in couples with relatively high intimate kiss frequencies. The microbiota on the dorsal surface of the tongue is more similar among partners than unrelated individuals, but its similarity does not clearly correlate to kissing behavior, indicating an important role for specific selection mechanisms resulting from a shared life style, environment, or genetic factors from the host. Our findings suggest that the collective bacteria among partners are able to multiply in the oral cavity, but some are only transiently present, while others have found a true niche on the tongue’s surface allowing long-term colonization. Keywords: Intimate kiss, oral microbiota, tongue, saliva, next generation sequencing, Streptococcus, Lactobacillus