Sexually Transmitted Microorganisms in Forensic Investigations: A Potential Tool

Sexual partners transfer their unique genital microbiota to one another during sexual intercourse. This can affect forensic investigations of sexual assault.

Brendan Chapman Murdoch University in Perth, Western Australia and his colleagues collected swabs from the genitals of 12 monogamous heterosexual couples and used RNA gene sequences to identify microbial signatures for each participant. Researchers asked couples to refrain from sex for two days to two weeks, and took follow-up samples several hours after sex.

“We found that these genetic signatures from female bacteria can be detected in male partners and vice versa,” Chapman says. As the team infused it, this change in a person's “sexome” could prove useful in criminal investigations, he says.

The amount of transfers varies from couple to couple, and the team found that even the use of condoms completely prevented the movement of the Sensomem from one partner to another. However, one major limitation of the outcome was the significant changes in female sexsomes during the period.

Chapman says there may be long-term homogenization of the microbiota of monogamous couples, but the bacterial population clearly differs between genders.

“The big advantage we have in our penis and vaginal microbiota is that we observe very different types of bacteria in each because there are huge differences in the two environments,” says Chapman. “For example, the penis is primarily a skin-like surface and therefore reflects similarity to the skin microbiota. There are a variety of anaerobic bacteria in the vagina, and the aerobic type in the penis. .”

So many of these bacteria cannot last indefinitely in the opposite environment, he says. “It's like comparing land to sea animals. Some live exclusively in one or the other and die if removed, but they willingly move and last.”

After establishing bacterial movement during sex, the team wants to prove that individual sexsomes are unique, like fingerprints and DNA. “I think every person's Sensomem contains enough diversity and uniqueness, but there's still something to do to demonstrate it with robust enough techniques to meet the forensic challenges. There is,” says Chapman.

If researchers can prove this, it can help investigate sexual assaults, particularly those in which male suspects do not ejaculate, have had vascular resections, or use condoms. “The genetic profile of a bacterial may be able to support or oppose propositions or testimony about what happened in the allegations of sexual assault,” he says. Dennis McNevin At Sydney Institute of Technology, Australia.

In such cases, the standard profile of human DNA is always preferred due to the great power of distinguishing individuals, he says, but sexomes may offer useful alternatives. “Bacterial genetic profiles may one day complement DNA evidence, or may help refer to the perpetrator of a rare sexual assault where DNA profiles are not available,” McNevin says.