Zhang Jun, Yu Daijing, Zhang Liwei, Wang Tian, Yan Jiangwei
School of Forensic Medicine, Shanxi Medical University, Jinzhong, Shanxi 030600, China; Shanxi Key Laboratory of Forensic Medicine, Jinzhong, Shanxi 030600, China.
School of Forensic Medicine, Shanxi Medical University, Jinzhong, Shanxi 030600, China; Shanxi Key Laboratory of Forensic Medicine, Jinzhong, Shanxi 030600, China.
Forensic Sci Int Genet. 2025 Jan;74:103170. doi: 10.1016/j.fsigen.2024.103170. Epub 2024 Oct 29.
The microbiome is a promising tool for identifying body fluids which can be deposited on various substrates at a crime scene. Body fluids collected from crime scenes are not entirely free from substrate microbes whose effects on the microbiome-based identification of body fluids are not well understood. In this study, five body fluids (peripheral blood, menstrual blood, nasal secretions, saliva, and semen) were deposited on sterile swabs, bedspreads, and floors under indoor exposure conditions for 7 days. The microbial communities in the samples were characterized using amplicon sequencing targeted V4 region of 16S rRNA gene. The results showed that the microbial communities of fresh samples deposited on sterile swabs clustered together according to the type of body fluid. The microbial composition of the body fluids deposited on the bedspread and floor is significant different from those deposited on sterile swabs. The microbial communities of mock body fluids were a mixture of microbes from pure body fluids and environmental microbes. FEAST analysis showed that the microbes of mock saliva samples were mainly from pure body fluids (51.53 % and 63.04 % on the bedspread and floor, respectively), but not from substrates (25.70 % and 18.92 % on the bedspread and floor, respectively). Contrary results were observed in peripheral blood, mock nasal secretion, and semen samples. All samples were mainly clustered based on the substrate, but not on the type of body fluid in the PCoA visualization. PERMANOVA results showed that the substrate accounted for more of the variance (R = 0.211, P < 0.001) than the type of body fluid (R = 0.152, P < 0.001). MicroDecon was used to remove contamination by microbes from the substrate of mock body fluid samples. PCoA and PERMANOVA were performed using decontaminated data. The results showed that samples were no longer clustered based on the substrate, and the type of body fluid (R = 0.240, P < 0.001) accounted for more of the variance in the microbial communities of samples than the substrate (R = 0.108, P < 0.001). Our results suggest that environmental microbiota from substrates may interfere with the microbiome-based identification of forensically relevant body fluids. To some extent, decontamination could decrease the effects of the substrate on the microbial communities of the samples and enhance the ability to distinguish between the types of body fluids. This pilot study will be valuable in promoting the application of microbiome-based stain analysis in forensics.
微生物群是一种很有前景的工具，可用于识别可能沉积在犯罪现场各种底物上的体液。从犯罪现场收集的体液并非完全没有底物微生物，而这些微生物对基于微生物群的体液识别的影响尚不清楚。在本研究中，将五种体液（外周血、月经血、鼻分泌物、唾液和精液）置于无菌拭子、床单和室内环境下的地板上暴露7天。使用靶向16S rRNA基因V4区域的扩增子测序对样本中的微生物群落进行表征。结果表明，沉积在无菌拭子上的新鲜样本的微生物群落根据体液类型聚集在一起。沉积在床单和地板上的体液的微生物组成与沉积在无菌拭子上的体液有显著差异。模拟体液的微生物群落是来自纯净体液的微生物和环境微生物的混合物。FEAST分析表明，模拟唾液样本中的微生物主要来自纯净体液（分别在床单和地板上占51.53%和63.04%），而非来自底物（分别在床单和地板上占25.70%和18.92%）。在外周血、模拟鼻分泌物和精液样本中观察到相反的结果。在PCoA可视化中，所有样本主要根据底物聚类，而非根据体液类型聚类。PERMANOVA结果表明，底物比体液类型解释了更多的方差（R = 0.211，P < 0.001）（R = 0.152，P < 0.001）。使用MicroDecon去除模拟体液样本底物中的微生物污染。使用去污染后的数据进行PCoA和PERMANOVA分析。结果表明，样本不再根据底物聚类，并且体液类型（R = 0.240，P < 0.001）比底物（R = 0.108，P < 0.001）在样本微生物群落的方差解释中占比更多。我们的结果表明，来自底物的环境微生物群可能会干扰基于微生物群的法医相关体液识别。在一定程度上，去污可以降低底物对样本微生物群落的影响，并增强区分体液类型的能力。这项初步研究对于促进基于微生物群的污渍分析在法医学中的应用将具有重要价值。
