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The necrobiome has been defined as the community of species associated with decaying remains after the death of an organism. The process of decomposition is complex. Microorganism decompose , but other including Fungus, , , and larger scavenger animals also contribute. Once the immune system is no longer active, microbes colonizing the intestines and decompose their respective tissues and then travel throughout the body via the Blood and to break down other tissue and bone. During this process, are released as a by-product and accumulate, causing bloating. Eventually, the gases seep through the body's and Body cavity, providing a way for some microbes to exit from the inside of the cadaver and inhabit the outside. The microbial communities colonizing the internal organs of a cadaver are referred to as the thanatomicrobiome. The region outside of the cadaver that is exposed to the external environment is referred to as the epinecrotic microbial communities of the necrobiome, and is especially important when determining the time and location of death for an individual. Different microbes play specific roles during each stage of the decomposition process. The microbes that colonize the cadaver and the rate of their activity are determined by the cadaver itself and the cadaver's surrounding environmental conditions.
Non-human animals only were dissected for anatomical understanding until the 13th century when officials realized human cadavers were necessary for a better understanding of the human body. It was not until 1676 that Antonie van Leeuwenhoek designed a lens that made it possible to visualize microbes, (2025). 9780062368607, HarperCollins Publishers. ISBN 9780062368607 and not until the late 18th century when microbes were considered useful in understanding the body after death.
In modern times, human cadavers are used for research, but other animal models can provide larger sample sizes and produce more controlled studies. (2025). 9781119062585, John Wiley & Sons, Ltd. ISBN 9781119062585 Microbial colonization between humans and some non-human animals is so similar that those models can be used to understand the decomposition process for humans. Pig have been used repeatedly to understand the human decomposition process in terrestrial environments. Pigs are suitable for studying human decomposition because of their size, sparse hairs, and similar bacteria found in their GI tracts. Using nonhuman carcasses as study subjects also offers the benefit of minimizing variation in the sample population.
Sophisticed molecular techniques have made it possible to identify the microbial communities that inhabit and decompose cadavers; however, this research is fairly new. Studying the necrobiome has become increasingly useful in determining the time and cause of death, which is useful in crime scene investigations.
Forensic investigate ways to determine time and place of death by analyzing the microbes present on the corpse. The microbial timeline of how a body decays is known as the microbial clock. It estimates how long a body has been in a certain place based on microbes present or missing. The succession of bacterial species populating the body after a period of four days is an indicator of minimum time since death. Recent studies have taken place to determine if bacteria alone can inform the post-mortem interval. Bacteria responsible for decomposing cadavers can be difficult to study because the bacteria found on a cadaver vary and change quickly. Bacteria can be brought to a cadaver by scavengers, air, or water. Other environmental factors like temperature and soil can impact the microbes found on a cadaver.
The time of death can be estimated not only by the type and amount of bacteria on a cadaver, but also by the chemical compounds produced by those bacteria. Forensic anthropologist Arpad Vass determined, from research he undertook in the 1990s, that three types of , produced when bacteria break down Adipose tissue, Skeletal muscle, and food remnants in the stomach are useful in predicting the time since death during forensic investigations.
Insect activity can also indicate the cause of death. Calliphoridae typically lay their eggs in natural body cavities that are easily assessible, yet also sheltered. If the pattern of maggot activity appears elsewhere, that could indicate an injury, such as a stab wound, even if the surrounding tissue has decomposed. In the event of a death caused by poison, traces of the toxin may have been consumed by the maggots, without harming them.
Since insect species tend to have certain Geography ranges and known habitat preferences, forensic entomologists can determine if a body has been moved after death. Analysis of the insects in the necrobiome can indicate if the death occurred in a different Ecological niche or geographical environment than where the cadaver was found.
In 2013, at the Southeast Texas Applied Forensics Science facility at Sam Houston State University, researchers documented the bacteria growing in two decomposing cadavers placed in a natural outdoor environment. Their focus was on the bloat stage, when hydrogen sulfide and methane produced by bacteria build up and inflate the cadaver. They found that "by the end of the bloat period...anaerobic bacteria such as Clostridia had become dominant" and swaps of the Mouth "showed a shift toward Bacillota, a group of bacteria that includes Clostridia."
By 2019, Jennifer Pechal, a forensic science researcher at Michigan State University, had worked with microbes on almost 2,000 human remains in a spectrum of conditions. She proposed a pattern in the necrobiome that concurs with data from scientists in Italy, Austria, and France. They found that a "large, consistent shift in the microbial community" occurs about 48 hours after death, making it "fairly easy to tell if a body has been dead for more or less than 2 days." Pechal also hopes that microbial tests can be used in the future to help Pathology determine undiagnosed medical conditions that were the cause of death.
Researchers are working on an algorithm to predict time since death with an accuracy of within two days, which would be an improvement over time frames given by forensic entomology. Jennifer Pechal states that those computer models must "be tested on bodies with a known time of death to ensure they are accurate." As of 2020, that technology is still 5 to 10 years away from becoming available.
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