Temporal Dynamics of Latent Fingerprint Microbiomes: A First Step to Decoding Crime Evidence

Background/Objectives: Latent fingerprints (LFs) have been a cornerstone of forensic identification through conventional friction ridge pattern analysis; however, the microbial communities they harbor remain a largely untapped source of information. Estimation of the time-since-deposition (TsDp) of LFs is still an unresolved challenge in forensic science, as existing 2D and 3D imaging methodologies provide limited temporal resolution. This study investigated whether temporal shifts in LF-associated microbiota could potentially complement dating approaches via genetic analyses. Methods: LFs were collected from two healthy donors from both hands, pre- and post-hand washing, across three time points spanning 192 h (8 days) under monitored, but uncontrolled, indoor conditions. LF friction ridges were optically examined via 2D and 3D imaging, while microbial communities were characterized by 16S rRNA gene sequencing targeting the V3-V4 region. Microbial profiles were analyzed to distinguish temporally stable core microbiota from transient taxa (alpha and beta diversity) and to statistically identify microbial panels associated with donor, handedness, hand-washing status, and/or temporal succession. Results: A stable core microbiota, dominated by Actinobacteria and Bacilli, persisted across donors, handedness, hand-washing status, and time points. Transient low-abundance taxa, including Nitriliruptoria and Phycisphaerae, exhibited temporal fluctuations influenced by donor characteristics, hand-washing status, and post-deposition interval. Upon excluding time-invariant stable taxa, donor-specific biological profiles comprising 32 and 28 class-rank taxa were selected for each donor, revealing individualized patterns of microbial dynamics. Conclusions: LF-associated microbiomes contain both stable and temporally dynamic taxa, with the potential to provide personalized biological information for TsDp estimation. These preliminary findings contribute to the molecular toolkit of forensic microbiomics by laying the foundation for prospective multimodal models integrating LF microbial and topographical data to improve the temporal interpretation of crime evidence touched by bare hands. Further validation with broader donor cohorts and environmental conditions are essential before operational forensic implementation.