Oral and skin microbiome as potential tools in the forensic field

The interest in the analysis of the human microbiome for personal identification purposes is founded on the microbial diversity amongst individuals. The oral cavity hosts one of the most diverse and abundant microbial communities in the human body; the skin instead is a complex living ecosystem with unique microbial niches at different sites. Both skin and oral microbiomes are highly individual and relatively stable over time. As saliva and skin debris are often found at crime scenes, the analysis of their microbiome may represent a potential tool for personal identification. However, there are some gaps in knowledge on how factors such as age, sex, geographic origin, diet and pathologies can affect the composition of the microbiome. The aim of this study is to improve the existing knowledge by examining oral and skin microbiomes from the same individuals and evaluating the variability between anatomical sites and individuals. Fifty Italian subjects of different sex and age were enrolled in the study. Oral swabs were taken together with information on diet, lifestyle and health status. In addition, the skin of the dominant hand was swabbed for 11 of the 50 individuals. DNA was extracted using the QIAamp PowerFecal Pro DNA Kit, and samples were quantified, amplified (hypervariable V4 region of the 16S rRNA gene) and sequenced via Illumina MiSeq. Data analysis was carried out with QIIME 2 and R. Results showed that the skin microbiome had more diverse bacterial communities, but less diversity between samples than the skin microbiome. Qualitative analyses on the oral microbiome showed relationships between the abundance of specific phyla and certain grouping conditions: Proteobacteria may reveal information on smoking habits; Spirochaetota and Synergistota may be biomarkers of age. This research outlines the potential use of oral and skin microbiome signatures as added evidence in personal identification, providing useful investigative clues for future forensic caseworks.