Advances in forensic DNA typing have enabled identification of individuals from just a few cells containing damaged human DNA. However, there remain cases where little or no human DNA can be recovered, limiting the amount of intelligence obtained. In these instances, biological traces still contain a complex mixture of non-human DNA originating from microorganisms present in the environment. Metagenomics enables the characterisation of this environmental DNA, offering a potential complementary source of forensic intelligence. 

Despite increasing interest, forensic applications of metagenomic profiling remain underexplored, particularly with respect to the stability and individuality of human-associated microbial communities. This study addresses this gap by investigating the temporal variability of touch-associated microbiomes and their potential to differentiate individuals over time. This provides critical insight into whether a stable, individualised microbial profile exists, which is a prerequisite for any downstream forensic intelligence application regarding transfer of these profiles.

A longitudinal sampling strategy was employed, in which multiple individuals were sampled across four seasons , with repeated sampling within each designated week. This design enabled both short-term and long-term variability in metagenomic profiles to be assessed. Samples were subjected to shotgun sequencing to best capture the full breadth of microbial communities present. Taxonomic classification was performed using Kraken, a k-mer-based approach for rapid assignment of sequencing reads to a taxon, with Bracken subsequently applied to refine these classifications.

These findings form the basis for future work examining the transfer and persistence of microbial signatures in forensic contexts. Establishing the degree of intra- and inter-individual variability is essential before such transfer dynamics can be meaningfully interpreted.

This research represents a novel contribution to forensic genetics by evaluating the stability of touch-associated metagenomic profiles within a longitudinal framework. By focusing on the feasibility of microbial profiling as an intelligence tool in cases where human DNA is absent or insufficient, this work lays the groundwork for expanding the forensic toolkit beyond traditional genetic markers.

Authors

• Ye Jee Roh (King's College London, United Kingdom)
• Lucinda Davenport (King's College London, United Kingdom)
• Robert Brownlow (King's College London, United Kingdom)
• David Ballard (King's College London, United Kingdom)