Conventional methods for testing sexual assault evidence are based on preferential lysis and rely on the presence spermatozoa to identify perpetrators. Low concentrations of male DNA and mixtures of perpetrator and victim DNA complicate profile interpretation. Consequently, evidence that screens negative for presence of semen, spermatozoa, or male DNA is often considered to have minimal probative value, leading to the termination of the workflow before DNA extraction to save time and resources. However, advancements in characterization and sequencing availability have opened up new possibilities for forensic analysis, particularly the identification of microbiomes. In recent years, the “Sexome”, or genital microbiome, has gained particular attention in hopes of filling the gap left by spermatozoa-focused analysis methods.
ISHI Student Ambassador, Julia Wang will be presenting on the above during her poster presentation at ISHI 34 this September. We chatted with her to learn a little more, and if you’ll be at the conference, be sure to stop by poster #58 to learn more!
Briefly describe your work/area of interest.
The motivation behind this project was to advance the application of 16S microbiome sequencing in the forensic examination of sexual assault evidence. Our goal was to establish a foundation for identifying the most effective extraction methods and to individualize the penile and microbiome profiles. This research aimed to enhance the forensic toolkit for sexual assault investigations.
This project is a brainchild of Sam Houston State University and Murdoch University in Perth, Australia. The work here at SHSU was started by a former student, Grace Rutledge, under Drs. Sheree Hughes and Rachel Houston. Our collaborators at Murdoch who helped with the conceptualization and bioinformatics are Brendan Chapman and Ruby Dixon. They recently published their proof-of-concept on their side of this “Sexome” project.
This study was designed to characterize genital microbiomes with an expectation of forensic application. Five different commercially available extraction and purification kits were compared to determine which would provide the highest and most representative yield for both commercial skin and vaginal microbial communities as well as those from donor penile and vaginal swabs.
Invitrogen™ PureLink™ Microbiome DNA Purification kit was found to be the best performing of the tested kits. The microbiome genera of the penile swabs were found to be more diverse than the vaginal swabs. As expected, Lactobacillus was the most abundant genus observed in the vaginal microbiome. Even so, unique genera were present in samples from most donors, highlighting the variability in microbiome composition. This potential for individualization will be explored in future studies of post-coital microbial transfer and persistence.
How did you get interested in this work? Why did this particular project appeal?
I was deeply intrigued by this project as it offered an opportunity to integrate next-generation sequencing into my dissertation, which already revolved around the analysis of sexual assault evidence. My interest was piqued during my extensive literature review, where I observed a growing trend in the forensic application of microbiomics. One noticeable gap in this knowledge landscape was the penile skin microbiome.
This project held great appeal to me because it represented the perfect convergence of acquiring and applying new technical skills to address an ongoing research gap in the realm of sexual assault evidence analysis.
Can you summarize the impact of your work for the audience (ISHI attendees and some general forensic enthusiasts)? How might this advance the field?
Because conventional methods for testing sexual assault evidence are based on preferential lysis and rely on the presence spermatozoa to identify perpetrators, this work offers an innovative approach through next-generation sequencing that can supplement traditional methods, enhancing the forensic toolkit available to crime labs in the absence of spermatozoa.
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