We know the microbiome varies greatly between individuals, but is it unique enough, and static enough, to be traced back to an individual? If it is, then it could theoretically be used to tie people back to the scene of a crime. Unfortunately not everyone defecates during their crimes, and bacteria transferred from skin can degrade rapidly. What about hair though? Hair is commonly obtained as evidence in many crimes because it possibly contains human DNA, however the majority does not. In these cases can the hair be analyzed for bacterial genomes, and then traced back to the perpetrator? A team of scientists from Australia sought to answer that question in a newly published article from the journal of Investigative Genetics.
Scalp and pubic hair was sampled from 42 individuals for the study. The findings showed that while each of the people shared common bacteria, they also contained many unique bacteria. Even with very little sampling depth, just identifying bacterial phyla, rather than genus or species, was enough to differentiate the people. This was especially true with pubic hairs, which were much more individualized than the scalp hair. In addition, the pubic hairs very clearly differentiated males and females based on the abundance of Lactobacillus, which are very abundant in female pubic hairs (as well as the vagina). Finally, the results showed that the hairs, especially pubic hairs, were stable over a 5 month span.
Overall this study serves as proof of concept for the microbiome being used as forensic evidence. This could especially be true for sexual assaults where there is no other physical evidence besides pubic hairs. Interestingly, the study found differentiation between people without characterizing bacterial species or strains. Higher resolution sequencing would almost certainly allow for higher discrimination in individuals. So a warning for all the criminals who read this blog, you may want to consider shaving before committing any felonies.