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Significant knowledge gaps exist regarding the responses of cells, tissues, and organs to organismal death. Examining the survival mechanisms influenced by metabolism and environment, this research has the potential to transform regenerative medicine, redefine legal death, and provide insights into life's physiological limits, paralleling inquiries in embryogenesis. 

Human death is a complex, time-governed phenomenon that leads to the irreversible cessation of all bodily functions. Recent molecular and genetic studies have revealed remarkable experimental evidence of genetically programmed cellular death characterized by several physiological processes; however, the basic physiological function that occurs during the immediate postmortem period remains inadequately described. There is a paucity of knowledge connecting necrotic pathologies occurring in human organ tissues to complete functional loss of the human organism. Cells, tissues, organs, and organ systems show a range of differential resilience and endurance responses that occur during organismal death. Intriguingly, a persistent ambiguity in the study of postmortem physiological systems is the determination of the trajectory of a complex multicellular human body, far from life-sustaining homeostasis, following the gradual or sudden expiry of its regulatory systems. Recent groundbreaking investigations have resulted in a paradigm shift in understanding the cell biology and physiology of death. Two significant findings are that (i) most cells in the human body are microbial, and (ii) microbial cell abundance significantly increases after death. By addressing the physiological as well as the microbiological aspects of death, future investigations are poised to reveal innovative insights into the enigmatic biological activities associated with death and human decomposition. Understanding the elaborate crosstalk of abiotic and biotic factors in the context of death has implications for scientific discoveries important to informing translational knowledge regarding the transition from living to the non-living. There are important and practical needs for a transformative reestablishment of accepted models of biological death (i.e., artificial intelligence, AI) for more precise determinations of when the regulatory mechanisms for homeostasis of a living individual have ceased. In this review, we summarize mechanisms of physiological, genetic, and microbiological processes that define the biological changes and pathways associated with human organismal death and decomposition. 

The decomposition of a body is inseparably associated with the release of several types of odors. This phenomenon has been used in the training of sniffer dogs for decades. The odor profile associated with decomposition consists of a range of volatile organic compounds (VOCs), chemical composition of which varies over time, temperature, environmental conditions, and the type of microorganisms, and insects colonizing the carcass. Mercaptans are responsible for the bad smell associated with corpses; however, there are no unified recommendations for conducting forensic analysis based on the detectable odor of revealed corpses and previous research on VOCs shows differing results. The aim of this review is to systematize the current knowledge on the type of volatile organic compounds related to the decomposition process, depending on a few variables. This knowledge will improve the methods of VOCs detection and analysis to be used in modern forensic diagnostics and improve the methods of training dogs for forensic applications. 

The study of the thyroid is an emerging topic, particularly in postmortem microbiome studies, due to the organ’s ability to affect the endocrine system. Also, the submandibular gland is a promising, emerging gland of study due to its position relative to the oral cavity. Previous thanatomicrobiome studies have demonstrated that bacteria belonging to the phyla Firmicutes, Proteobacteria, Bacteroides, and Pseudomonadota predominate internal organs and have been considered an important biomarker for postmortem interval. Further, Clostridium species that dominate in internal organs are linked to the hypoxic change that occurs after death, which leads to the switch of bacteria to become obligate anaerobes. Therefore, obligate anaerobes dominate the body after death due to their ability to thrive off fermentation products. 16S rRNA gene sequencing has been critical in thanatomicrobiome studies, which refers to the human microbiome (microorganisms within the body) after death. Currently, it has not been elucidated regarding the microorganisms that are associated with the decay of submandibular and thyroid glands. We hypothesized that through sequencing of the 16S rRNA gene of the submandibular and thyroid glands, the presence of Firmicutes and Proteobacteria will indicate potential biomarkers for postmortem interval. The present study revealed the postmortem microbial signatures of the submandibular and thyroid glands using the 16S rRNA gene, specifically the V3-V4 hypervariable regions, using universal primers 341F and 805R. We investigated a total of 37 cadavers obtained from ongoing criminal casework, 17 submandibular samples and 20 thyroid samples, and found that there is a correlation between microbial abundance in these postmortem glands. The predominating phyla of interest found in both glands were Firmicutes and Proteobacteria. The predominating genera were Paeniclostridium and Streptococcus in both glands, respectively. Further experimentation of the submandibular and thyroid glands will help to link oral thanatomicrobiome communities to “microbial clock” determinations, thus enhancing postmortem interval estimation. 

The microbiota gut-brain-axis is a bidirectional circuit that links the neural, endocrine, and immunological systems with gut microbial communities. The gut microbiome plays significant roles in human mind and behavior, specifically pain perception, learning capacity, memory, and temperament. Studies have shown that disruptions in the gut microbiota have been associated with substance use disorders. The interplay of gut microbiota in substance abuse disorders has not been elucidated; however, postmortem microbiome profiles may produce promising avenues for future forensic investigations. The goal of the current study was to determine gut microbiome composition in substance abuse disorder cases using transverse colon tissues of 21 drug overdose versus 19 non-overdose-related cases. We hypothesized that postmortem samples of the same cause of death will reveal similar microbial taxonomic relationships. We compared microbial diversity profiles using amplicon-based sequencing of the 16S rRNA gene V4 hypervariable region. The results demonstrated that the microbial abundance in younger-aged cases were found to have significantly more operational taxonomic units than older cases. Using weighted UniFrac analysis, the influence of substances in overdose cases was found to be a significant factor in determining microbiome similarity. The results also revealed that samples of the same cause of death cluster together, showing a high degree of similarity between samples and a low degree of similarity among samples of different causes of death. In conclusion, our examination of human transverse colon microflora in decomposing remains extends emerging literature on postmortem microbial communities, which will ultimately contribute to advanced knowledge of human putrefaction. 

Forensic laboratories are required to have analytical tools to confidently differentiate illegal substances such as marijuana from legal products (i.e., industrial hemp). The Achilles heel of industrial hemp is its association with marijuana. Industrial hemp from the Cannabis sativa L. plant is reported to be one of the strongest natural multipurpose fibers on earth. The Cannabis plant is a vigorous annual crop broadly separated into two classes: industrial hemp and marijuana. Up until the eighteenth century, hemp was one of the major fibers in the United States. The decline of its cultivation and applications is largely due to burgeoning manufacture of synthetic fibers. Traditional composite materials such as concrete, fiberglass insulation, and lumber are environmentally unfavorable. Industrial hemp exhibits environmental sustainability, low maintenance, and high local and national economic impacts. The 2018 Farm Bill made way for the legalization of hemp by categorizing it as an ordinary agricultural commodity. Unlike marijuana, hemp contains less than 0.3% of the cannabinoid, Δ9-tetrahydrocannabinol, the psychoactive compound which gives users psychotropic effects and confers illegality in some locations. On the other hand, industrial hemp contains cannabidiol found in the resinous flower of Cannabis and is purported to have multiple advantageous uses. There is a paucity of investigations of the identity, microbial diversity, and biochemical characterizations of industrial hemp. This review provides background on important topics regarding hemp and the quantification of total tetrahydrocannabinol in hemp products. It will also serve as an overview of emergent microbiological studies regarding hemp inflorescences. Further, we examine challenges in using forensic analytical methodologies tasked to distinguish legal fiber-type material from illegal drug-types. 

Death is a universal phenomenon and what happens after life has led to extensive forensic ecology research. Consequently, we now know that the shell of the once living provides fertile ground for other life forms, spanning prokaryotic microbes to large, vertebrate scavengers. This ephemeral patch of newly available resources also provides rich sources of evidence that can be used in death investigation. In recent years there have been substantial advances in technology that have facilitated the research and application of human remains decomposition in ways that harness theory and basic understanding of the ecological and evolutionary sciences (Tomberlin et al., 2011). To that end, this special issue covers the most recent perspectives and research that explores the complex ways that the once living can provide important information to the forensic sciences, in ways that can ultimately be applied to the judicial system and its processes. It is within this context of linking basic research in death and decomposition to applications of forensics that the special topic was born. 

In this century, drug abuse continues to be a national crisis. Since 1999, the number of opioid-induced overdoses has increased four-fold to more than 500,000 deaths. The microbiota gut-brain-axis is a bidirectional circuit that links the neural, endocrine, and immunological systems with gut microbial communities. Gut microbiota play significant roles in human mind and behavior, specifically pain perception, learning capacity and memory, mood, and emotion, and anxiolytic effects and temperament. Also, disruptions in the gut microbiome have been associated with substance use disorders. While much research still needs to be performed, elucidating the interplay of gut microbiota in substance abuse disorders may produce promising avenues for future forensic development. The goal of the current study was to determine gut microbiome composition in substance abuse disorder cases using transverse colon tissues of 21 overdose criminal cases versus 19 non-overdose-related cases. The hypothesis was that postmortem samples of the same origin will reveal similar taxonomic relationships. Using weighted UniFrac analysis, drug abuse was found to be a significant factor in determining microbiome similarity (F = 1.93; df = 1, 35; p < 0.048; R2 = 0.05) indicating that there are detectable differences in composition that are attributable to substance abuse. Using unweighted UniFrac, however, sex was instead found to be a significant predictor of microbiome similarity (F = 1.88; df = 1, 30; p = 0.028; R2 = 0.05). A heatmap was generated of the relative abundances of the 30 most prevalent bacteria per case and their associated substance profile. The results revealed that samples of the same origin cluster together, showing a high degree of similarity between samples and a low degree of similarity among samples of different origin. This examination of human transverse colon microflora in decomposing cadavers expands the emerging literature on postmortem microbial communities, which will ultimately contribute to advanced knowledge of putrefaction. 

Italy and the United States are two of the countries most affected by SARS-CoV-2 (COVID-19), with more than 240,760 confirmed cases in Italy and 2,699,658 in the United States (as of July 2, 2020). The current COVID-19 pandemic has led to substantial changes in many fields of medicine, specifically in the forensic discipline. Medicolegal activities related to conducting autopsies have been largely affected by the COVID-19 pandemic. Postmortem examinations are generally discouraged by government regulations due to the risk of spreading the disease further through the handling and dissection of bodies from patients who succumbed to COVID-19 infection. There is a paucity of data regarding the persistence of SARS-CoV-2 in bodies, as well as concerning the reliability of swabbing methods in human remains. On the other hand, the autopsy is an essential tool to provide necessary information about the pathophysiology of the disease that presents useful clinical and epidemiological insights. On this basis, we aim to address issues concerning general medical examiner/coroner organization, comparing the Italian and American systems. We also discuss the pivotal roles of forensic pathologists in informing infectious disease surveillance. Finally, we focus on the impact of COVID-19 emergency on medicolegal practices in Italy and the United States, as well as the responses of the forensic scientific community to the emerging concerns related to the pandemic. We believe that stronger efforts by authorities are necessary to facilitate completing postmortem examinations, as data derived from such assessments are expected to be paramount to improving patient management and disease prevention. 

Human thanatomicrobiota studies have shown that microorganisms inhabit and proliferate externally and internally throughout the body and are the primary mediators of putrefaction after death. Yet little is known about the source and diversity of the thanatomicrobiome or the underlying factors leading to delayed decomposition exhibited by reproductive organs. The use of the V4 hypervariable region of bacterial 16S rRNA gene sequences for taxonomic classification (“barcoding”) and phylogenetic analyses of human postmortem microbiota has recently emerged as a possible tool in forensic microbiology. The goal of this study was to apply a 16S rRNA barcoding approach to investigate variation among different organs, as well as the extent to which microbial associations among different body organs in human cadavers can be used to predict forensically important determinations, such as cause and time of death. We assessed microbiota of organ tissues including brain, heart, liver, spleen, prostate, and uterus collected at autopsy from criminal casework of 40 Italian cadavers with times of death ranging from 24 to 432 h. Both the uterus and prostate had a significantly higher alpha diversity compared to other anatomical sites, and exhibited a significantly different microbial community composition from non-reproductive organs, which we found to be dominated by the bacterial orders MLE1-12, Saprospirales, and Burkholderiales. In contrast, reproductive organs were dominated by Clostridiales, Lactobacillales, and showed a marked decrease in relative abundance of MLE1-12. These results provide insight into the observation that the uterus and prostate are the last internal organs to decay during human decomposition. We conclude that distinct community profiles of reproductive versus non-reproductive organs may help guide the application of forensic microbiology tools to investigations of human cadavers.