Exploring human related bacterial communities for forensic applications in human profiling and death investigations

Abstract

Advances in sequencing technologies have revolutionised forensic science, expanding the types of evidence that can be extracted from crime scenes. Human related microbiomes, encompassing the bacterial communities living on and within the body, as well as those in the surrounding environment, hold tremendous promise for forensic applications. This thesis investigates the use of microbiomes for human profiling purposes. It also explores the role of the microbiome in decomposition across different burial contexts – relating to grave type (single or mass graves), burial depth, and human and/or animal decomposition. This research explores the utility of human related microbiomes in addressing the aforementioned aims and proposes the microbiome as a complementary tool to traditional methods.

First, the human oral microbiome was explored for its potential in predicting geographic origin by assessing its variability within a country, and between countries. Studies revealed some intra-country regional differences and significant inter-country variation (across six countries – Nigeria, Italy, South Africa, Thailand, USA and China), highlighting the microbiome’s potential for geographic profiling. A follow-up study on the effects of migration demonstrated possible microbial adaptations to environmental changes, showing short-term shifts following relocation and reversion to native profiles over the period assessed.

Secondly, decomposition experiments – setup in Preston, UK and Texas State, USA – focused on microbial community succession over time in both controlled pig models and human cadavers. Additionally, freezing studies explored the impact of frozen human cadaver preservation on associated microbial communities, ensuring accurate representation of natural decomposition processes when previously frozen cadavers are utilised in research. Furthermore, a novel focus on microbiomes in mass graves revealed distinct grave soil microbial taxa in comparison to single/individual burials and alluded to a reduced decomposition rate in a grave containing multiple remains. These findings suggest the need for adjusted post burial interval calculations in mass burial contexts and the potential of grave soil microbiomes indicators of grave type.

By addressing these gaps in knowledge of human associated microbiomes in living and post-mortem contexts, this thesis demonstrates its potential in assisting forensic investigations. These findings advance the field of forensic microbiology, paving the way for future interdisciplinary research and the integration of microbiome analysis into routine forensic practice.

Date of Award	22 May 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Darren Smith (Supervisor) & Andrew Nelson (Supervisor)