Microbial population analysis improves the evidential value of faecal traces in forensic investigations

Abstract

The forensic science community has a growing interest in microbial population analysis, especially the microbial populations found inside and on the human body. Both their high abundance, microbes outnumber human cells by a factor 10, and their diversity, different sites of the human body harbour different microbial communities, make them an interesting tool for forensics. Faecal material is a type of trace evidence which can be found in a variety of criminal cases, but is often being ignored in forensic investigations. Deriving a human short tandem repeat (STR) profile from a faecal sample can be challenging. However, the microbial communities within faecal material can be of additional criminalistic value in linking a faecal trace to the possible donor. We present a microarray technique in which the faecal microbial community is used to differentiate between faecal samples and developed a decision model to predict the possible common origin of questioned samples. The results show that this technique may be a useful additional tool when no or only partial human STR profiles can be generated.

The Future of Environmental DNA in Forensic Science

“…As with other prediction methods, subsequent testing on additional samples not used for model training and from additional individuals will be important. A similar approach was developed for forensic applications, specifically targeting certain microbial taxa within feces, to provide additional information about the source/material type and to potentially discriminate individuals (35). Probes targeting a selection of microbial taxa were designed to yield a feces-specific signature to be applied to samples of unknown origin and to assess whether the signature was indeed fecal in origin and whether the overall microbial signature varied between samples (35).…”

“…A similar approach was developed for forensic applications, specifically targeting certain microbial taxa within feces, to provide additional information about the source/material type and to potentially discriminate individuals (35). Probes targeting a selection of microbial taxa were designed to yield a feces-specific signature to be applied to samples of unknown origin and to assess whether the signature was indeed fecal in origin and whether the overall microbial signature varied between samples (35). While further validation work is required, this method was applied to supplement human genotyping in two casework instances and proved to be a useful additional investigative tool for the identification of cell/material type (36).…”

“…Human identification using microbial profiles is generally proposed as an approach to complement traditional profiling using human DNA markers when human DNA could not be recovered or the data quality was low (32,35). However, many variables still need to be assessed to appropriately evaluate the potential of such microbe-based identification methods, ideally using samples collected from large numbers of individuals.…”

Massively parallel sequencing is unlocking the potential of environmental trace evidence

“…Benschop et al 2012 used 16S rRNA V5 and V6 to explore the microbiota in 240 clinical vaginal samples and used this to develop a more targeted microarray for determining vaginal origin [112]. Similarly, Quaak et al 2017 developed a targeted microbial microarray approach to differentiate faecal samples from multiple individuals and thus link a question sample to a particular donor [113], which has since been expanded and successfully applied in two cases, (a sexual assault and a robbery) to determine the sub-source of question samples [114]. Saliva, body fluid, faecal matter and hair samples represent sources of relatively high microbial biomass, whereas skin-associated microbiomes transferred to objects via touch represent low biomass samples and are therefore more challenging.…”

Challenges in Human Skin Microbial Profiling for Forensic Science: A Review

“…Within the body of research investigating the potential forensic utility of skin microbiomes as trace evidence, a significant proportion of studies involve the analysis of bacterial communities through targeted sequencing of the 16S ribosomal RNA (rRNA) region [ 12 , 15 , 16 , 34 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. This region is conserved within bacteria, but harbours enough interspecific variation to allow different bacterial species to be discerned through sequencing [ 48 ].…”