Human-associated microbial populations as evidence in forensic casework.

Area of Science:

• Microbiology
• Forensic Science
• Genomics

Background:

• Cell type identification is crucial in forensic investigations to verify scenarios.
• Existing methods primarily focus on human molecular characteristics.
• A novel approach is needed to complement current forensic cell typing techniques.

Purpose of the Study:

• To develop and evaluate a microarray method for human cell type identification based on associated microbial populations.
• To assess the method's ability to distinguish between different human body sites and animal origins.
• To validate the microarray approach using mock forensic samples.

Main Methods:

• Design and implementation of a microarray with 863 probes targeting microbial species, genera, and families.
• Analysis of 175 human samples from various body sites (hand, foot, groin, penis, vagina, mouth, faeces).
• Inclusion of feline and canine faeces samples for comparative analysis.
• Application of clustering and classification algorithms for data interpretation.

Main Results:

• Clear differentiation of faecal and oral samples from vaginal and skin samples.
• Successful discrimination between human, canine, and feline faeces.
• Variable classification of penis samples (similar to vaginal or skin samples).
• Challenges in discriminating between different skin sample sites.
• High accuracy in classifying mock case samples, with minor misclassifications in sub-clusters.

Conclusions:

• The microbial population-based microarray method is a valuable addition to existing forensic cell typing techniques.
• This method provides independent targets, complementing techniques like mRNA typing.
• Combining microbial analysis with other methods can significantly increase the evidential value of forensic traces.