Metagenomic analyses of bacteria on human hairs: a qualitative assessment for applications in forensic science

Abstract

BackgroundMammalian hairs are one of the most ubiquitous types of trace evidence collected in the course of forensic investigations. However, hairs that are naturally shed or that lack roots are problematic substrates for DNA profiling; these hair types often contain insufficient nuclear DNA to yield short tandem repeat (STR) profiles. Whilst there have been a number of initial investigations evaluating the value of metagenomics analyses for forensic applications (e.g. examination of computer keyboards), there have been no metagenomic evaluations of human hairs—a substrate commonly encountered during forensic practice. This present study attempts to address this forensic capability gap, by conducting a qualitative assessment into the applicability of metagenomic analyses of human scalp and pubic hair.ResultsForty-two DNA extracts obtained from human scalp and pubic hairs generated a total of 79,766 reads, yielding 39,814 reads post control and abundance filtering. The results revealed the presence of unique combinations of microbial taxa that can enable discrimination between individuals and signature taxa indigenous to female pubic hairs. Microbial data from a single co-habiting couple added an extra dimension to the study by suggesting that metagenomic analyses might be of evidentiary value in sexual assault cases when other associative evidence is not present.ConclusionsOf all the data generated in this study, the next-generation sequencing (NGS) data generated from pubic hair held the most potential for forensic applications. Metagenomic analyses of human hairs may provide independent data to augment other forensic results and possibly provide association between victims of sexual assault and offender when other associative evidence is absent. Based on results garnered in the present study, we believe that with further development, bacterial profiling of hair will become a valuable addition to the forensic toolkit.

Microbial forensics: new breakthroughs and future prospects

“…Hairs are amongst of the most commonly found evidence collected at crime scenes. However, the vast majority lacks the anagenic root (actively growing hair), essential for DNA extraction and posterior analysis employing conventional typing methods, such as STR profiles (Tridico et al 2014;Tridico et al 2017).…”

The Future of Forensic Biology

“…The vast microbial communities (bacteria, yeast and viruses) remain same except after sex. Therefore in future, the pubic hair recovered from sexual assault suspects if do not contain the roots, then the metagenomic analysis of microbes in the hair may become a substitute of evidence [36]. The microbes and hence the microbial DNA differs in males and females and therefore after sex, the microbes in both the male and the female appear to swap, indicating that a sexual act occurred between a particular man and woman.…”

The future of forensic DNA analysis

“…Biogeographic ancestry estimation may be helpful in some case scenarios [54]. Microbial DNA may also play a role in future investigations to lend support to circumstances involving microbial transfer when touching a computer keyboard [55] or having sexual intercourse [56]. This analysis will likely be performed with NGS or other high-throughput methods in the future.…”