The ability to detect traces of human DNA on touched objects and in areas of close proximity is well established. However, forensic applications are often limited by the low quantity and degraded nature of touch DNA. An emerging and relatively underexplored approach to associate individuals with objects or environments is the analysis of microbiome traces. In addition to human DNA, individuals continuously deposit microbial signatures into their surroundings. As human-associated microbiomes are partly individualized, they may provide valuable information for linking individuals to specific locations or objects.

To investigate the transfer, persistence, prevalence, and recovery (TPPR) of human microbiomes and their potential utility in forensic casework we collected samples from ten households in the Oslo region. To characterize the indoor microbial environment, two environmental sample types were obtained: air samples collected from kitchens using the AirPrep ACD220 electret filter sampler after all occupants had vacated the premises, and surface samples from commonly touched areas collected using moistened swabs. In addition, personal items (participants’ mobile phones) were sampled. To assess secondary transfer, a sterile screwdriver was placed in a common room in the houses for one week before being retrieved and sampled. In total, 71 environmental samples were collected.

All adult participants (n = 21) provided reference microbiome samples, including buccal swabs, two skin swabs, one from the upper arm and one from the neck, and textile samples obtained by tape-lifting worn garments.

To maximize DNA yield from air filters, a modified version of the DNeasy PowerWater Kit (Qiagen) was selected following pilot testing. Microbial community composition was characterized by amplicon sequencing targeting the V4 region of the 16S rRNA gene. Libraries were sequenced on an Illumina MiSeq FGx using the Verogen MiSeq FGx Reagent Micro Kit (Qiagen). Microbiome profiles were analyzed using random forest classifiers trained separately on reference and household samples to evaluate their ability to assign individuals, objects, and sample types to the correct household.

This dataset represents a comprehensive and well-controlled study of microbiome TPPR in indoor home environments, contributing to a still limited body of forensic research. By combining diverse sample types, controlled transfer experiments, and matched reference profiles, the study is uniquely positioned to assess the evidential potential of microbiome traces. The project provides critical knowledge on the feasibility of microbiome-based inference in forensic casework, and inform future methodological development in the field.

Authors

• Aurora Hofsvang (Oslo University Hospital, University of Oslo, Norway)
• Eric Jacques de Muinck (University of Oslo, Norway)
• Eirik Natås Hanssen (Oslo University Hospital, Norway)
• Ane Elida Fonneløp (Oslo University Hospital, University of Oslo, Norway)