Tiny Traces, Big Impact: Fingertip Microbiomes in Forensic and Pathology Research”,

Microorganisms are ubiquitously present on both interior and exterior human body surfaces, outnumbering human cells 3:1.1 Like human DNA shed from skin cells, microbes are also transferred to the environment.2,3 The circular structure of bacterial DNA and peptidoglycan walls makes it highly preserved, resisting degradation better than human DNA. Microbiome analyses are becoming increasingly relevant in forensics for individual identification, and fingerprints contain enough microbial DNA to create trustworthy profiles.2 This presentation explores semi-standardized recovery of microbiomes from fingertips. This pilot study examines the potential of fingertip microbiomes to reveal biologically and forensically relevant inter-individual differences. Specifically, it investigates whether distinct microbial signatures correlate with sex (male vs. female), handedness (dominant vs. non-dominant), and medical conditions like celiac disease or gluten intolerance. The goal is to evaluate microbial profiles’ discriminatory power for identifying individuals and inferring physiological or pathological traits. Findings may offer new insights into forensic microbiology, where microbial traces could complement medico-legal evidence. Twenty donors (10 male and 10 female) were enrolled in the study. Volunteers were allowed to choose their usual mode of transportation to the laboratory (e.g., walking, subway, bus, or private vehicle). Upon arrival, a trained operator collected a sample from each single donor’s fingertip of both the dominant hand (DH) and non-dominant hand (NDH) using dried Self Skin FLOQSwabs.4 Participants then completed a lifestyle questionnaire. Total DNA was extracted using the Qiagen QIAamp DNA Blood and Tissue Kit, allowing for the co-isolation and quantification of both human and microbial DNA.5 Following the protocols recommended by the Human Microbiome Project, the V4 region of the 16S rRNA gene was PCR-amplified and sequenced using the Illumina MiSeq System. The resulting FASTQ files were imported into QIIME2 (version 2024.5.0) for processing. Quality filtering and denoising were performed using the DADA2 plugin (QIIME2 DADA2 denoise-paired), and sequences were trimmed accordingly. Taxonomic classification was conducted using the SILVA 138-99 reference database. Downstream analyses were performed in R (version 4.2.3) using the ‘phyloseq’ package. Microbiome profiles were successfully typed for all out of 200 samples. Interestingly, it was possible to consistently identify unique taxa on all ten fingertips from an individual that were not detected in any other donors within the group. These unique taxa may have relevance for personal identification studies and may be useful to provide forensic intelligence information also when “touch DNA” fails. Additionally, the fingertip microbiome across the ten fingers of an individual is relatively consistent, but differs significantly between individuals, including distinctions based on sex.3 Furthermore, the study revealed significant differences between 'nonpathological' donors and those with food-related conditions such as celiac disease or gluten intolerance, as well as between alcohol consumers and non-consumers, and between individuals who commuted to work on foot versus those using public transportation. During the presentation, a detailed comparison of the donors' results will be provided, focusing on the microbial signatures identified among participants and their potential application in forensic investigations.