This is a summary report on a project that developed a method of estimation of postmortem interval (PMI) - the time elapsed since a person's death - based on the composition of microbial communities present on the body and within close-proximity soil samples compatible to intervals of days to months.
The project found that microbial communities can accurately determine body PMI up to 48 days since death, with an average error of about 3 days. It identified "universal" microbial markers for determining PMI, despite the environment. The method developed identifies environmental conditions that can affect microbial communities' composition, such as temperature, location, and season. Further, the project determined the potential for microbial signatures that assist in identifying clandestine gravesites. The research team characterized temporal changes in microbial communities on the skin of mice, pigs, and human cadavers at fixed PMIs. It collected, sequenced, and classified 223 abdominal cavity, skin, grave soil, and no-corpse soil samples. It created a dataset of over 2.9 million 16S rRNA sequences that represent 4505 Operational Taxonomic Units. This is a unit used to represent microbial "species" at various taxonomic levels in the microbial community, based on sequences similarity. Next-generation rRNA sequencing demonstrated that groupings of microbial species change as a body undergoes the various stages of decomposition. The team used the data to develop a regression model for PMI estimation, concluding that microbial communities changed predictably as the corpse decomposed. Future related planned research is briefly described.