The ‘sexome’, bacterial DNA makeup of the sex organs, was discovered by Murdoch University PhD candidate Ruby Dixon in 2023 as part of research conceptualised by forensic scientist Dr Brendan Chapman. 

This new research presents that the sexome not only confirms intercourse taking place but also leaves behind ‘trace’ or ‘transfer’ samples unique to a person.  

There were 36,318 recorded victims of sexual assault in Australia in 2023 – with the victimisation rate increasing from 126 to 136 victims per 100,000 persons. The need for increasingly robust investigation tools is indispensable.  

Dr Chapman said knowledge from this study would provide additional support to the ‘DNA toolkit’ investigators use to identify perpetrators 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,” Dr Chapman said.  

The great thing about our approach is that it doesn’t require any additional sampling or trauma to a victim. That’s important to us. 

Participants in ongoing sexual relationships (heterosexual) were recruited for the study and initial samples taken during periods of abstinence provided researchers with a snapshot of the DNA associated with healthy bacterial communities surrounding their genitals.  

The couples then had sex and took a second series of samples in the hours following intercourse.  

When comparing the before and after samples, researchers could see bacterial DNA signatures transferred between partners.  

Next steps for the research will be assessing how the baseline vaginal microbiome changes over time.  

“For example, the menstrual cycle brings many physiological changes to the environment that affect bacteria – so mapping that is important,” Dr Chapman said.  

“The other reality is that often, following sexual assault, it is many hours, sometimes days, before a victim is seen by a doctor. Our understanding of how long we can delay sampling is limited at this stage also. 

“This is all part of our plan for Ruby’s PhD and potentially beyond that.” 

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