Most forensic research that is used to better understand how to estimate the postmortem interval (PMI) entails the study of the physiochemical characteristics of decomposition and the effects that environmental factors have on the decomposition process. Forensic entomology exploits the life cycles of arthropods like Diptera (blow flies or flesh flies) and Coleoptera (beetles) deposited on the decaying carcass to determine PMI. Forensic taphonomy, from the Greek word taphos meaning burial, studies the creation of the fossils of decomposed cadavers to ascertain information as to the nature and time of death. Compared to other areas of taphonomy, there have been relatively few forensic science studies that have investigated the impact of human decomposition on the microbial changes occurring on or in a corpse or in the soil communities underneath a body. Such research may facilitate the critical determination of PMI. Therefore, the scope of this review is to provide a concise summary of the current progress in the newly emerging field of microbial diversity and the next-generation metagenomic sequencing approaches for assessing these communities in humans and in the soil beneath decomposing human.

Microbial communities associated with human decomposition and their potential use as postmortem clocks

When postmortem intervals (PMIs) increase such as with longer burial times, human remains suffer increasingly from the taphonomic effects of decomposition processes such as autolysis and putrefaction. In this study, various DNA analysis techniques and a messenger RNA (mRNA) profiling method were applied to examine for trends in nucleic acid degradation and the postmortem interval. The DNA analysis techniques include highly sensitive DNA quantitation (with and without degradation index), standard and low template STR profiling, insertion and null alleles (INNUL) of retrotransposable elements typing and mitochondrial DNA profiling. The used mRNA profiling system targets genes with tissue specific expression for seven human organs as reported by Lindenbergh et al. (Int J Legal Med 127:891-900, 27) and has been applied to forensic evidentiary traces but not to excavated tissues. The techniques were applied to a total of 81 brain, lung, liver, skeletal muscle, heart, kidney and skin samples obtained from 19 excavated graves with burial times ranging from 4 to 42 years. Results show that brain and heart are the organs in which both DNA and RNA remain remarkably stable, notwithstanding long PMIs. The other organ tissues either show poor overall profiling results or vary for DNA and RNA profiling success, with sometimes DNA and other times RNA profiling being more successful. No straightforward relations were observed between nucleic acid profiling results and the PMI. This study shows that not only DNA but also RNA molecules can be remarkably stable and used for profiling of long-buried human remains, which corroborate forensic applications. The insight that the brain and heart tissues tend to provide the best profiling results may change sampling policies in identification cases of degrading cadavers.

DNA and RNA profiling of excavated human remains with varying postmortem intervals.

Decomposition is degradation process of a corpse into basic respective constituents macroscopically and microscopically by action of microorganisms, arthropods and scavengers. Post mortem changes could be separated into early post mortem changes (i.e. algor mortis, rigor mortis and livor mortis) and putrefaction stages of corpse. These changes function as suitable indicators for determination of post mortem interval (PMI). In this paper, different stages of post mortem changes, possible variations such as mummification and formation of adipocere and special circumstances such as burial condition is discussed. This article also refers to several arguments in the different texture of adipocere and the influence of different types of fabric in affecting the post mortem changes and formation of adipocere. This is largely due to the property of permeability and resistance of material against degradation process. Undeniably, decomposition process involves numerous potential variables including burial condition, presence of clothing, potential formation of adipocere and mummification. Hence, studies in forensic taphonomy combined with real case scenario are crucial in understanding the nature of decomposition and estimation of PMI with higher accuracy.

Decomposition Process and Post Mortem Changes: Review

Estimation of post-mortem time interval (PMI) is a key parameter in the forensic investigation which poses a huge challenge to the medico-legal experts. The succession of microbes within different parts of the human body after death has shown huge potential in the determination of PMI. Human body harbors trillions of microorganisms as commensals. With the death of an individual when biological functions are stopped, these microorganisms behave contrarily along with the invasion of degrading microbes from the environment. Human cadaver becomes a rich source of nutrients due to autolysis of cells, which attracts various invading microorganisms as well as macroorganisms. At different stages of degradation, the succession of microorganisms differs significantly which can be explored for accurate PMI estimation. With the advent of microbial genomics technique and reduction in the cost of DNA sequencing, thanatomicrobiome and epinecrotic community analysis have gained huge attention in PMI estimation. The article summarizes different sources of microorganisms in a human cadaver, their succession pattern, and analytical techniques for application in the field of microbial forensics. KEY POINTS: • Thanatomicrobiome and epinecrotic microbiome develop in postmortem human body. • Lack of metabolic, immune, neuroendocrine systems facilitate microbial succession. • Analysis of postmortem microbial communities predicts accurate PMI.

Thanatomicrobiome and epinecrotic community signatures for estimation of post-mortem time interval in human cadaver

Potential applications of soil microbial ecology and next-generation sequencing in criminal investigations

Post mortem changes are important in estimating post mortem interval (PMI). This project's aim was to study the effect of burial and type of clothing on rate of decomposition, which can contribute to estimating PMI for victims. 12 rabbits (Oryctolagus cuniculus) carcasses were separated into 3 groups: no clothing, light clothing and heavy clothing. Control subjects were placed on the ground surface while test subjects were buried at 30 cm depth graves. Soil samples prior and after decomposition were collected for soil pH and moisture analysis. Post mortem change was assessed using a Total Body Score system. The head, neck and limb regions were found to decay faster than the body trunk region. Mummifi cation occurred on body parts that were exposed directly to the atmosphere while adipocere formed on some buried subjects. Burial delayed decomposition due to lower insect activity and lower soil temperature. The soil layer also blocked the accessibility of majority of the arthropods, causing further delay in decomposition. Clothing enhanced decay for bodies on ground surface because it provided protection for maggots and retained moisture on tissues. However, clothing delayed decomposition in buried bodies because it physically separated the bodies from soil and arthropods. Higher sun exposure and repetitive exhumation showed acceleration of decomposition. The decomposition process increased soil pH and moisture percentage values. Soil pH initially increased until pH 8.0-8.4 followed by a slight decrease while soil moisture percentage changed inconsistently. Burial was significant in affecting post mortem change, F(1,11)=12.991, p<0.05 while type of clothing was not significant, F(2,9)=0.022, p=0.978 and combination of both type of clothing and burial factors were also not significant, F(2,3)=0.429, p=0.686. For validation, an accuracy of 83.33% was achieved based on soil pH and soil moisture percentage analysis.

/pdf/post-mortem-changes-in-relation-to-different-types-of-53qhj5e740.pdf

Post mortem changes in relation to different types of clothing.

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Decomposition Process and Post Mortem Changes: Review

Post mortem changes in relation to different types of clothing.