Our genital microbiota or "sexome" is unique and could be used to identify rape perpetrators like a bacterial fingerprint, Australian scientists explain in a study published in the journal iScience.
Study participants rub long cotton swabs inside their vaginas, along their penises, and around the glans. The 12 volunteer couples took the swabs after at least two to 14 days of abstinence, and then a few hours after heterosexual intercourse with penetration. When we compared the before and after samples, we could see bacterial DNA signatures from the woman on the man and from the man on the woman." explains Brendan Chapman, a forensic science researcher at Murdoch University in Australia. In forensics, this is what we call a "trace" or a "transfer" and it is this type of evidence that we ultimately use to demonstrate that contact has occurred.. »
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The Limits of Semen Detection After Rape
When a victim of a sex crime comes forward, forensic science laboratories take male biological material from the female victim during an examination by a doctor who specializes in sexual assault. This method is extremely effective", says Brendan Chapman, but in practice the search for and isolation of spermatozoa " pose some problems“.
First, the sample must be taken within 48 hours of the incident, otherwise the proportion of spermatozoa will be significantly lower in vaginal samples. In addition, the processing of the sample to separate the sperm from the other cells and then purify the DNA does indeed result in losses. Not counting scenarios where there are no sperm, such as when an offender does not ejaculate, is vasectomized or uses a condom", adds the researcher.
Female sexoma is detected on the penis even with a condom
This is where the sexome, the genital microbiota, can be a useful complementary tool in cases where conventional DNA tests do not work. To achieve this, we need to understand which bacteria will make suitable targets." explains Brendan Chapman. According to their observations, bacteria of the type Lactobacillus contributed the most to the transfer of the female sexome to the male sexome. It is also the bacterial genus most found in the vaginal microbiota.
Condom use, lubricant use, frequency of oral sex, circumcision and pubic hair had no statistically significant impact on microbial diversity in either men or women, the scientists report. In contrast, when a condom was used, the majority of microbial transfer was from women to men, although the reverse was true. be possible", comments Brendan Chapman. While the reasons for this relatively one-sided transfer are not known, the researcher suspects that " The way the condom is put on and the activities that took place beforehand can serve as a vector for the transfer of the bacteria“.
Potential persistence of transfers even several days after intercourse
This discovery means that there may be microbial markers that can detect sexual contact, even when a condom is used, the researchers point out in the publication. Especially since they detected a DNA signature of a man's partner in samples taken after five days of abstinence. We hypothesize that this could be residual traces of previous sexual contact, in which case it would have persisted for a number of days and despite washing.", hopes Brendan Chapman, who will devote future work to it. The advantage of our approach is that it does not require any additional sampling or trauma to the victim. This is an important point for us." he concludes.
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