The relevance and value of hair as Forensic evidence gained importance in nineteenth century. Durability and stability are the key qualities that renders mammalian hair structures important as biological structures. The extreme hardiness is due to the presence of protein called keratins. Let us look in detail about the DNA Microbial Profiling of Bacteria in Hair Analysis with the following diagram.
Historical Perspectives of Hair in Forensic Analysis
Transmitted light Microscopy plays a very important role in Forensic Investigation. Microscopy of hair analysis associated the offender to the crime involved in the untimely death of an elderly women. The beginning of human DNA profiling using STR result shift the way how forensic hair samples are processed. Human hair contain variable amount of nuclear DNA and ability to obtain STR DNA profile depends upon the growth phase of hair root.
Mammalian hair samples undergoes three stages of growth cycle.
Actively embedded in the follicle and difficult to dislodge it. Hir roots and tissues are source of nuclear DNA.
Roots represents ephemeral growth phase in which hair growth enters quiescent phase and results in the concomitant loss of nuclear DNA.
Roots represent final growth stage in which hair ceased to grow. Telogen hair roots are poor source of nuclear DNA but remain rich in mtDNA. Hairs identified in anagen or catagen growth phase are successfully processed for nuclear DNA STR profiling.
Research into hair Microbiomes
The beginning of Next Generation Sequencing investigated the potential value of Bacterial DNA Profiling in Hair analysis. Khodakova et al evaluated discrimination of soil based on bacterial inhabitants. Lax et al explored forensic potential of bacteria that colonize telephones and shoes to discriminate between individuals.
Hair Sample, collection, storage and Isolation of microbial DNA
The advent of PCR in Forensic Investigation the community developed stringent protocols to ensure integrity of bio evidence. Forensic Biological evidence such as hairs often starts in the crime scene which might be outdoors or in building. Collection of hair samples from suspect, victim and other related individual is important. Hairs are collected from scalp and pubic hairs. Pubic hairs are less frequently used in Investigation. All evidence require long or short term storage post collection. Dry biological evidence should be sealed in paper, sealed plastic bags or in envelopes to ensure the integrity of evidence.
DNA sequencing of hair microbiomes
Bacterial analysis fallen into two categories. Metagenomic Analysis is to identify which organism is there and Metatranscriptomic analysis is used to identify what they are doing. The genomic analysis of human bacteria in Forensic Investigation is very important. Selection of primers are necessary inorder to maximize microbial data from hair samples. Human DNA profiling plays a very important role in Forensic Investigation. Microbial DNA profiling involves inter or multidisciplinary approaches in the interpretation of data and evidences in the court. The collabrators includes Forensic practitioners, Microbiologists and Bioinformatics. The challenging aspect is the coordination and presentation of information in the court.
The assessment of scalp and pubic hair is a novel forensic technique. The other legal issues includes laboratory contamination issues, statistical analyses.Research studies conducted by Tridico et al (2014) showed that scalp and pubic hairs showed the presence of microbes inhabiting these two niches. Genomic Analyses should focus on the use of universal primers to conduct Bacterial audits in hair analysis. Future work is to develop methodology based on bacterial Single Nucleotide Polymorphisms. Potential of microorganisms is gaining prominence in Forensic community. Preliminary results in human hair DNA profiling requires more detail analysis and the results should be reported.