The bacterial composition of our genital microbiome is as unique as we are, and it's transferred during sex, according to new research. Just like a fingerprint, the so-called "sexome" may help identify sexual offenders, even in cases where a condom is used.
We know from research into the gut microbiome that the specific composition and proportions of the microbial communities we house are unique to each of us, like a fingerprint. What about microbiomes in other parts of our bodies? Are they just as unique, and could they be used forensically?
A new study led by Australian researchers from Murdoch University, the University of Western Australia, and The Kids Research Institute suggests that the answer to all of these questions is ‘yes’ when it comes to the genital microbiome – which the researchers dubbed the "sexome."
“This research is based on the forensic concept that every contact leaves a trace,” said forensic scientist Brendan Chapman, chair of the School of Medical, Molecular and Forensic Sciences at Murdoch University and the study’s senior author. “Until now, few studies have explored the vaginal and penile microbiomes within a forensic context. This research demonstrates that we can observe microbial traces for heterosexual couple’s genital microbiomes following sex.”
Sexual violence against women remains a significant public health and safety concern. The World Health Organization (WHO) estimates that, globally, about one in three women have been subjected to either physical and/or sexual intimate partner violence or non-partner sexual violence in their lifetime. While individuals of all biological sexes, gender identities, and sexual orientations can experience sexual violence, research consistently shows that women face a significantly higher risk.
Anyone who has ever watched a police crime drama knows that the collection of DNA evidence left on the body following a sexual assault – the sexual assault forensic exam or sexual assault evidence kit (SAEK), often called a ‘rape kit’ – is crucial to the investigative process. However, retrieving and isolating male DNA and adequately separating it from female DNA in these cases can be challenging. So, the researchers investigated the possibility of using the genital microbiome – the sexome – as an alternative.
They recruited 12 monogamous heterosexual couples aged between 20 and 30 to investigate whether the sexome was transferred during penetrative sex, including when a condom was used. At the start of the study, each participant swabbed their genitals to provide a baseline sample of their ‘down there’ microbiome. Using RNA gene sequencing, the researchers determined what bacterial strains were present, right down to the sub-species, and identified each participant’s microbial signature. The couples were asked to abstain from sex for between two and 14 days before having penetrative sexual contact as part of the study. After sex, sexome samples were again collected from each participant so they could be analyzed.
Comparing before- and after-sex samples, the researchers observed a noticeable disruption to microbial diversity in both male and female participants, although it wasn’t consistent across all couples. Investigating microbial diversity further, they found that one partner’s sexome could be identified on the other partner, suggesting a transfer of their unique bacterial signature during sex. They also noted a transfer of non-unique bacteria in all couples.
Whether the men were circumcised, whether pubic hair was shaved or intact, whether couples engaged in oral sex or used a lubricant, and whether a condom was used – none of these factors had a statistically significant impact on the microbial diversity of the sexome. Interestingly, in terms of condom use, the researchers found that the majority of microbial transfer occurred from the female to the male.
“This shows promise for a means of testing a perpetrator post-assault and means there may be microbial markers that detect sexual contact even when a condom was used,” the researchers said. “The results of this research show that microbiome analysis may have some utility in [the] investigation of sexual assault cases as an additional tool when male DNA is not present for traditional … profiling to occur.”
Future research will focus on how long the transferred sexome persists after sexual contact and how long it takes for the genital microbiome to return to baseline after being disrupted by sex.
The study was published in the journal iScience.
Source: Cell Press via Scimex
