The identification of biological traces provides vital evidence in forensic reconstruction at crime scenes, especially in sexual offences. Compared with traditional presumptive or confirmatory methods, the microbiome-based method has been proven to be of great value in body fluid identification. Mixture of body fluids or tissue is common in sexual assault cases; thus, it is essential to determine the sources of mixed samples. In this study, 60 samples consisting of skin, saliva, and a mixed model of saliva deposited on facial skin were collected from a population living in Guangdong. Through 16s rDNA high-throughput sequencing, we identified the predominant microbes in saliva samples, viz., Haemophilus parainfluenzae T3T1, Neisseria flava, Gemella haemolysans, Prevotella melaninogenica, and Actinomyces odontolyticus; in skin samples, Cutibacterium acnes and Corynebacterium tuberculostearicum were the predominant species. The microbial composition of the same body fluid or tissue is similar in different individuals. However, among different body fluids or tissue, the composition of microflora in saliva is more stable than that on skin. Additionally, the microbial community in the mixed model of saliva deposited on facial skin from the same and different individuals was clearly determined by the constituent fluids or tissue, apart from the differences among the donors. Overall, the microbiome-based method may have good potential as a tool for identifying single and mixed body fluid or tissue.
Keywords: Body fluid and tissue identification; Forensic genetics; High-throughput sequencing; Microbiome; Mixed body fluid or tissue.