The Microbiome of Human Decomposition

Deep in the primordial forest of eastern Texas, we watch our team of undergraduate and graduate students taking swab samples from a pair of human cadavers that we placed at the Southeast Texas Applied Forensics Science (STAFS) facility of Sam Houston State University (SHSU) in Huntsville. Our highly choreographed sampling regime, which focuses on bacterial communities, includes swabbing seven body sites on each cadaver, collecting nearby soil samples, tabulating temperatures, and collecting cadaver-associated flies. We do this daily until the bodies begin to dry out, then sample every other day for another month, then once weekly for yet another month, then once per month for 6 months until only dry bones remain. We continue taking soil samples for approximately one year longer. Each team includes about 10 students per sampling visit, and their efforts take about 10 minutes to complete. As part of a project that was funded through the National Institute of Justice, an agency of the federal Department of Justice, we placed a pair of human bodies each season for three years and collected more than 20,000 samples. The challenges associated with studying how microorganisms drive human decomposition stem from many factors. However, by analyzing the microbial communities involved in every stage of cadaver decomposition, we can gain a more precise understanding of the overall process. Knowing the identity and succession of those bacterial communities not only provides insights into the overall process but can also aid in determining the postmortem interval when dealing with unidentifıed remains. Such research responds to a 2009 report, “Strengthening Forensic Science in the United States,” from the National Research Council of the National Academy of Sciences. It urges researchers in disparate disciplines, including microbiology, entomology, chemistry, and the forensic sciences, to work together to develop a comprehensive model for describing the cadaver decomposition process.