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 searchable male profile. While 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. Human microbiome research has suggested that a person’s microbial diversity is unique. An adjunct method of perpetrator identification lies with microbiome analysis using next generation sequencing.
This study aimed to identify bacteria taxa that were unique to each participant and compare the bacterial communities found on the genitals pre- and post-coitus. 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.
Samples were collected from 14 male-female pairings across two recruitment cohorts. Volunteers were asked to self-collect low vaginal (females) and shaft and glans (males) samples pre- and post-coitus. Samples were extracted using PureLink™ Microbiome DNA Purification Kit. Extracted DNA underwent library preparation using primers targeting the and V1-9 hypervariable regions of the bacterial 16S rRNA gene (~1,449 bp). Libraries were sequenced by the PacBio® SMRT Sequel II sequencing platform. 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. The couple who did not use a barrier contraceptive yielded the most microbial transfer and disruption to diversity. A transfer of the female microbiome during intercourse was most significant. 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.