Bacterial Communities Associated with Human Decomposition
Human decomposition is a little-understood process with even less currently known about the microbiology involved. The aim of this research was to investigate the bacterial community associated with exposed decomposing mammalian carcasses on soil and to determine whether changes in this community could potentially be used to determine time since death in forensic investigations. A variety of soil chemistry and molecular biology methods, including molecular profiling tools T-RFLP and DGGE were used to explore how and when bacterial communities change during the course of a decomposition event. General bacterial populations and more specific bacterial groups were examined. Decomposition was shown to cause significant and sequential changes in the bacterial communities within the soil, and changes in the bacterial community often correlated with visual changes in the stage of decomposition. Organisms derived from the cadavers and carcasses were able to be detected, using molecular methods, in the underlying soil throughout the decomposition period studied. There was little correlation found between decomposition stage and the presence and diversity within the specific bacterial groups investigated. Organisms contributing to the changes seen in the bacterial communities using molecular profiling methods were identified using a cloning and sequencing based technique and included soil and environment-derived bacteria, as well as carcass or cadaver-derived organisms. This research demonstrated that pig (Sus scrofa) carcass and human cadaver decomposition result in similar bacterial community changes in soil, confirming that pig carcasses are a good model for studying the microbiology of human decomposition. The inability to control for differences between donated human cadavers made understanding the human cadaver results difficult, whereas pig carcass study allowed many variables to be held constant while others were investigated. The information gained from this study about the bacteria associated with a cadaver and how the community alters over the course of decomposition may, in the future, enable the development of a forensic post mortem interval estimation tool based on these changes in the bacterial community over time. The findings in this thesis suggest that high variability between human bodies and their microflora is likely to present a challenge to the development of such a tool, but further study with emerging high-throughput molecular tools may enable identification of microbial biomarkers for this purpose.