Move over DNA – genital bacteria ‘sexome’ could be used to identify rapists

When you get down and dirty with it, your bacteria like to spread themselves around.

That’s the message of a new study of the ‘sexome’ published in the journal  Forensic Science International, and the researchers suggest that our unique bacterial colonies could be used in sexual assault and rape cases where DNA can’t be found.

 “Current techniques for investigating sexual assault work well, however if there aren’t enough male cells then there may not be enough to link it to a person using conventional DNA analysis,” Murdoch University forensic scientist Ruby Dixon says.

“This research shows that we can detect that a heterosexual couple has had intercourse based on the bacteria we find after sex.”

The researchers collected bacterial samples from six heterosexual couples before and after they’d had sex.

After looking at the bacterial transfer, they found “a significant disruption to microbial diversity post-coitus in all samples”. In simple terms – the bacteria had migrated.

The one couple who did not use a barrier contraceptive (like a condom) had the most transfer, meaning that testing the microbiome could be used in some sexual assault cases.

“Some ‘male bacteria’ stays on the female and some ‘female bacteria’ stays on the male,” says Dixon.

“The end goal is that we’ll be able to take a swab, analyse the bacteria, and link it back to an individual, or at the very least eliminate suspects.”

The biggest changes were between Lactobacillus, which dominated (98%) the female samples before intercourse, while Lactobacillus only made up about a quarter of the male bacterial make up. Unfortunately, the second most abundant genera on the penile samples was Staphylococcus (13%).

“Although male bacteria may look relatively similar at a glance, we found the composition of each person’s bacterial makeup is probably different enough to use for identification,” says Dixon.

More research will need to be done to check if this could be a helpful tool for law enforcement.

“We’ve demonstrated the concept, and the plan is to further investigate uniqueness of individual bacterial fingerprints and the effect of things like contraception and non-heterosexual couples,” says Murdoch University Forensic scientist Brendan Chapman.

“Bacteria may be just as powerful as conventional forensic DNA but with the added benefit of being available even when male human DNA is undetectable.”