Human bodies are home to vast microbial ecosystems. New research from Murdoch University in Australia reveals that during sexual contact, individuals exchange unique bacterial communities from their genital microbiomes, what the scientists call the “sexome.”
The researchers found that a person’s unique genital bacteria transfer to their partner and linger. These findings could lead to a new forensic tool, offering an additional method for identifying suspects in sexual assault cases. “In forensic science we work on the concept that all contact leaves a trace behind. With fingerprints that’s obviously the residues from our skin and in the case of the sexome, we’re using the healthy bacterial communities living on, and within, our bodies as a means of detecting that transfer,” explained senior researcher Brendan Chapman, a forensic scientist at Murdoch University.
Reading Bacteria Like a Book
Our bodies teem with bacteria. One way scientists analyze these microbial communities is by sequencing a segment of ribosomal RNA called 16S. In the past, technology could only read short fragments of 16S, giving researchers a rough idea of the bacteria present. However, newer sequencing methods allow for a more detailed picture.
“We now have more advanced systems for massively parallel sequencing that can analyze longer strings of that 16S gene region, meaning we have a better view of the unique signatures within the community,” Chapman said. “It’s a bit like the difference between only knowing the names of chapters within a book, compared to being able to read the words on the page.”
The research team studied 12 monogamous, heterosexual couples. First, they mapped each person’s baseline sexome. Then, the couples refrained from sex for between 2 to 14 days. After resuming sex, researchers analyzed their microbiomes again. The results, published in iScience, were clear: bacterial signatures from one partner were detectable on the other.
The Evidence Sticks
The study found that pubic hair and circumcision status did not significantly impact bacterial transfer. Condom use reduced the transfer of male bacteria to the female partner, but the female’s bacteria still appeared on the male. This suggests that sexome analysis could help identify perpetrators of sexual assault, even when a condom is used.
More work is needed to refine the technique. Menstruation appeared to alter a woman’s microbiome, raising questions about how these changes affect bacterial transfer. Scientists also need to determine how long swapped bacteria remain traceable.
While acknowledging that the research is still preliminary, the researchers say the findings may eventually be used to support investigations of sexual assault. “We propose that the sexome can be used as another tool in the forensic DNA toolkit, to either strengthen the validity of human DNA findings or to be used when that technique comes up short,” Chapman said in a statement.
Beyond Forensics
Understanding the sexome could have other benefits beyond crime-solving. Scientists already know the gut microbiome affects digestive health, and the sexome may play a similar role in reproductive health.
“The greater our understanding of the relationship we have with our bacterial passengers, the better we can utilize them for improving health outcomes,” Chapman said. “We already know how important the gut microbiome is to digestive health, and the same is likely true for the sexome—providing protective features for the vaginal microenvironment and maybe even fertility.”
The research is just beginning, but one thing is clear: when it comes to microbial sexual exchange, understanding bacterial signatures may have important implications.
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