Sexual partners transfer their distinctive genital microbiome to each other during intercourse, a finding that could have implications for forensic investigations of sexual assault.

at Murdoch University in Perth, Western Australia, and his colleagues collected swabs from the genitals of 12 monogamous, heterosexual couples, then used RNA gene sequencing to identify microbial signatures for each participant. The researchers asked the couples to abstain from sex for between two days and two weeks, and took follow-up samples a few hours after intercourse.

鈥淲e found that those genetic signatures from the female鈥檚 bacteria were detectable in their male partners and vice versa,鈥� says Chapman. This change in a person鈥檚 鈥渟exome鈥�, as the team has dubbed it, could prove useful in criminal investigations, he says.

The amount of transfer varied from couple to couple, and the team also found that not even condom use completely prevented the movement of the sexome from one partner to another. However, one major limitation of the results was that the female sexome changed significantly during a period.

Chapman says that even though there may be some homogenisation of the microbiomes of long-term, monogamous couples, the bacterial populations clearly differ between the sexes.

鈥淭he great benefit we have with the penile and vaginal microbiomes is that because of the vast difference in the two environments, we observe very different bacteria types on each,鈥� says Chapman. 鈥淔or example, the penis is mostly a skin-like surface and thus reflects similarities with the skin microbiome. We see anaerobic bacteria types in the vagina and aerobic types on the penis.鈥�

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As such, many of these bacteria can鈥檛 persist indefinitely in the opposite environment, he says. 鈥淚t鈥檚 a bit like comparing land and sea animals 鈥� there are some that exclusively live in one or the other location and would die if removed, but also some that happily move between and persist.鈥�

Having established the transfer of bacteria during intercourse, the team is now hoping to prove that an individual鈥檚 sexome is unique, like a fingerprint or DNA. 鈥淚 think there鈥檚 enough diversity and uniqueness contained within everyone鈥檚 sexome, but there鈥檚 still a bit of work to do in order for us to demonstrate that with a technique that is robust enough to meet the challenges of forensic science,鈥� says Chapman.

If the researchers are able to prove this, it could aid in sexual assault investigations, particularly ones in which a male suspect doesn鈥檛 ejaculate, has had a vasectomy or uses a condom. 鈥淏acterial genetic profiles might be able to corroborate or oppose propositions or testimonies about what happened in alleged sexual assault cases,鈥� says at the University of Technology Sydney, Australia.

Standard profiles of human DNA will always be prioritised in such cases because of their great power to differentiate between individuals, he says, but the sexome could offer a useful alternative. 鈥淏acterial genetic profiles may one day complement DNA evidence or may even help point to a perpetrator of a sexual assault in the rare cases where DNA profiles are not available,鈥� says McNevin.

Artificial intelligence can accurately identify whether or not fingerprints left by different fingers came from the same person. This could help forensic investigators uncover if one individual was present at separate crime scenes.

Current technologies are only capable of matching fingerprints left by the same finger. But previous studies have hinted there may be fundamental similarities between all of a person鈥檚 fingertips.

So, at Columbia University in New York and his colleagues trained a machine learning model to determine if it could identify whether fingerprints from different fingers belong to the same person. In the training, they used more than 50,000 fingerprints from almost 1000 people. Samples came from public databases at the US National Institute of Standards and Technology and the University at Buffalo in New York. All fingerprints belonged to deceased individuals or had been de-identified from people still alive.

The team then tested the trained model on a separate set of more than 7000 fingerprints from approximately 150 people. They evaluated the model using a statistical measure that estimates accuracy on a scale of 0 to 1. The researchers found their model scored greater than a 0.75, suggesting it reliably identifies whether or not prints from different fingers belong to the same person.

This technology could enhance the efficiency of forensic investigations. 鈥淚t could be useful in cases where you have fingerprints found at multiple crime scenes, which don鈥檛 match to anybody in databases,鈥� says at Pennsylvania State University. 鈥淐ould the person who left the fingerprints at this particular crime scene be the same person who left [different] prints at this other crime scene?鈥�

However, 鈥渞ight now the accuracy isn鈥檛 high enough [for this model] to decide this in the court of law鈥�, says Guo.

鈥淚f this thing is used in practice, for legal purposes, it should be retrained with a [bigger] database,鈥� says , also at Columbia University and part of the research team.