The "sexome", our intimate microbiome, equivalent to DNA in criminal investigations 🕵️

The traces left by sexual intercourse are not limited to DNA. A study reveals that each individual has a unique genital microbiome, called the "sexome", which could serve as evidence in criminal investigations.

In cases of sexual assault, the analysis of sperm DNA is often used. However, this method has limitations, particularly when a condom is used or in the absence of ejaculation. A team of Australian researchers proposes an alternative: the study of the genital microbiome, or "sexome". Published in iScience, their research shows that genital bacteria are transferred between partners during sexual intercourse, even with a condom.

The sexome, a unique microbial signature

Each individual has a distinct genital microbiome, a community of specific bacteria that colonizes the intimate areas. This composition, called the "sexome", varies from person to person, offering a microbial signature as unique as a fingerprint. To study this phenomenon, researchers analyzed samples from 12 heterosexual couples before and after sexual intercourse.

The results showed that the microbial signatures of the partners were detectable in each other after intimate contact. Even after several days, traces of these bacterial exchanges remained identifiable thanks to advanced genetic sequencing techniques. This discovery confirms that the sexome can serve as a biological marker to prove sexual contact.

The use of a condom does reduce the transfer of bacteria, but does not eliminate it completely. In these cases, the majority of exchanges occur from the woman to the man, likely due to the proximity of the contact areas and the specific bacterial composition of the vaginal microbiome. This observation suggests that even with a condom, microbial traces could be used to identify an assailant, offering a valuable alternative when sperm DNA is lacking.

Promising applications in forensic medicine

The sexome could become a valuable tool to complement current DNA analysis techniques, particularly in cases where traditional evidence, such as the presence of sperm, is insufficient. This method relies on the analysis of the genital microbiome, a unique microbial fingerprint for each individual. Researchers emphasize that this approach does not require additional sampling, which minimizes trauma for victims of sexual assault.

However, several factors can influence the composition of the genital microbiome, complicating its use in forensic medicine. For example, the menstrual cycle alters the diversity and abundance of vaginal bacteria, which can affect the results of analyses. Other factors, such as personal hygiene or the use of intimate products, could also alter microbial traces. These variables require in-depth research to refine the technique and ensure its reliability.

Scientists plan to study the persistence of microbial traces after sexual intercourse, an essential piece of data for its application in a judicial context. They also seek to determine how long these traces remain detectable and how they evolve over time. In parallel, studies on larger and more diverse samples, including non-heterosexual couples, are planned to validate the robustness of this method.

To go further: What is the genital microbiome?

The genital microbiome refers to all the microorganisms, mainly bacteria, that colonize the intimate areas. In women, it is dominated by bacteria of the Lactobacillus genus, known for their protective role. These bacteria maintain an acidic environment, which helps prevent infections. In men, the genital microbiome is less abundant but more diverse, with a variety of specific bacterial strains.

The composition of the genital microbiome is influenced by many factors, such as age, personal hygiene, sexual practices, and even diet. For example, a diet rich in probiotics can promote the presence of beneficial bacteria. On the other hand, excessive use of intimate hygiene products can disrupt this balance, making the individual more vulnerable to infections.

The genital microbiome plays a key role in reproductive and sexual health. In women, it helps prevent urinary tract infections and sexually transmitted diseases. In men, it could influence fertility and sperm quality. Recent research also suggests a link between a healthy genital microbiome and a better local immune response.

Finally, the genital microbiome is unique to each individual, making it a potentially usable microbial fingerprint in forensic medicine. This uniqueness opens the door to innovative applications, such as identifying assailants in cases of sexual assault, even in the absence of traditional DNA evidence.