The sexome A proof of concept study into microbial transfer between heterosexual couples after sexual intercourse
The capture of male DNA, post-assault, is important in sexual assault investigation, particularly where an offender is unknown to the victim. The recovery of DNA often occurs when the female victim undergoes a forensic medical assessment. Analysis regularly results in mixed autosomal DNA profiles. As these results contain both victim and perpetrator DNA, they are often difficult to interpret a male profile suitable for DNA database searching. While short tandem repeat (STR) profiling of the male Y-chromosome is often used to overcome this, the successful identification of an individual can be hindered by the paternal inheritance pattern of Y-STRs as well as smaller Y-STR databases. Human microbiome research has suggested that a person's microbial diversity is unique. An adjunct method of perpetrator identification lies with microbiome analysis using massively parallel sequencing (MPS). This study aimed to identify bacteria taxa that were unique to each participant and compare the bacterial communities found on their genitals; pre- and post-coitus. Samples were collected from six male-female sexual partner pairs. Volunteers were asked to self-collect low vaginal (females) and penis shaft and glans (males) samples before and after intercourse. Samples were extracted using the PureLink Microbiome DNA Purification Kit. Extracted DNA underwent library preparation using primers targeting the V3-V4 hypervariable regions of the bacterial 16S rRNA gene (~450 bp). Libraries were sequenced on the Illumina MiSeq platform. From the sequence data derived, statistical analysis was performed to investigate if bacteria sequences could be used to infer contact between each male-female pairing. Unique bacterial signatures were detected in low frequencies (<1%) in male and female participants pre-coitus. The data indicates a significant disruption to microbial diversity post-coitus in all samples. A transfer of the female microbiome during intercourse was most significant. One couple who did not use a barrier contraceptive yielded the most microbial transfer and disruption to diversity demonstrating a proof-of-concept in the utility of microbiome interrogation for sexual assault cases. Further genomic analysis is needed to confirm species and subspecies classification of bacteria that may produce a unique microbial profile that could be used to identify a specific individual.