Hair is the maximum common evidence that can be determined without difficulty on every second crime scene at some point of forensic investigation.

However, there may be a massive opportunity that the hair discovered at the crime scene may also lack their roots and genetic material due to which, wearing out DNA profiling of the suspect isn't possible.

These days, In maximum of the sexual assault cases, suspect uses ‘condom’ and take it away after the attack.

Because of using condoms, the risk of exposure to sperm or genes is negligible.

Another approach for tracking suspects based on the hair left at the crime scene is to detect the microorganisms present on the hair.

There are different microbial communities, or microbiotas living in different areas of our body.

In the first forensic study of the hair bacteria, researchers gave their preliminary results that they can distinguish between men, women and individuals based on bacteria present on their pubic hair, so pubic hair in particular has the greatest potential for forensic research.

They also found that the microbiota of human pubic hair appeared to have been transferred during sexual intercourse, suggesting the possibility of forensic analysis of sexual assault cases.

The implications of this current study may be that bacterial transmission between victims and perpetrators in rape cases may provide a new way of associating perpetrators with victims in the cases where human DNA is not transferred.

In a small study, researchers asked seven people (two of them were couple who were living together) to collect their scalp and pubic hair for five months.

The researchers then analysed these samples in the lab to look for the bacterial populations that were present at 2 and 5 months.

Scalp hair indicates that 50 types of microorganisms were found in men and 55 types in women in this part of the body, but many of the microorganisms found were not unique to the person who carried them.

However, pubic hair bacteria turned out to be more pronounced. In addition, each person's "personal" genital bacteria remained about the same throughout the five months.

More types of bacteria live in these hairs: about 73 for men and 76 for women. This study suggests that more combinations of different bacteria means that the people are more likely to have unique microbial characteristics.

Although each pubic hair bacterium was different for all the seven people but a higher similarity of pubic hair bacterium were found in the pubic hair of cohabiting couples at 5 months than found at 2 months.

The couple later revealed that they had sexual intercourse 18 hours before collecting their hair. The result was "far from being definitive based on bacteria", as there was only one couple living together and only seven participants in total.

Max Houck, Senior Forensic Scientist at the Consolidated Forensic Laboratory, a Washington, D.C.-based government agency, agrees.

However, he also points out that it may be more difficult to use this method if there was previous sexual contact between the victim and the individual, for example in the case of an abusive ex-spouse.

He also mentioned that "Human pubic hair bacterium can be of a potentially important use if the victim and the subject have never had sexual contact before."

Rachel Fleming, a molecular biologist at the Institute of Environmental Science and Research Ltd., a government research institute based in Auckland, New Zealand, says further research is needed to use pubic hair bacteria in forensic investigations and some experiments should be conducted to determine how easily bacteria can be transmitted between humans, whether they can be transmitted using the same bed, clothing, or towels, and how long the transmitted bacteria stay in the pubic hair.

Hair Microbiota

Bacteria that inhabit male and female scalp samples and pubic hair are classified as “primary” or “transient” (Tr) bacteria.

In relation to the number of OTUs (Operational Taxonomic Unit) extracted from scalp and pubic hair microbiomes, far less bacterial sequences were lost post control filtering for pubic microbiomes in comparison to scalp hair. In general, pubic hair contains more OTUs than scalp hair (compared to about 50 male OTUs/55 females for scalp hair, compared to about 73/76 for pubic hair).

Thus, in general, the pubic microbiome appears to be less susceptible to environmental bacteria than scalp hair and may contain more niche-specific bacteria.

Therefore, in general, pubic hair bacteria is less influenced by environmental bacteria than scalp hair and possible harbour more niche specific bacteria. Zhou et al. supported this premise by demonstrating that the vaginal microbiome (relative to other parts of the body) consists of more stable bacteria (i.e., less transient bacteria) and exhibits lower alpha diversity (i.e., bacteria).

1. Pubic Hair Microbiota

Male pubic hair is easily distinguishable from female pubic hair according to their respective microbiota.

Lactobacillus was the most common taxon that clearly distinguished male and female pubic microbiota.

Fleming and Harbison suggested that two species of Lactobacillus spp. exist. (Lactobacillus crispatus and Lactobacillus gasseri) used as suitable forensic markers for the identification of vaginal secretions.

However, the microbiological data obtained from this study suggest that the metagenomic NGS(next-generation sequencing) approach may be better than those targeting specific species.

Fewer transient bacteria were present in female pubic hair compared to male pubic hair, and the number of bacterial sequences containing transient bacteria in female pubic hair was approximately half that of male pubic hair.

This discrepancy may be because probiotics provide "antibacterial protection" to the vagina, preventing colonization by other microorganisms.

Lee Myung-bak and others also found that in comparison to other body areas, the vaginal microbiome is less transient (i.e. more stable). This stability was evident in the difference in the amount of OTUs found in the scalp and pubic controls, and the pubic controls had significantly fewer OTUs compared to the scalp.

2. Scalp Hair Microbiota

In contrast to the pubic hairs, scalp hair bacteria showed no mutual relationship with the sex of the donor.

Male and female scalp hair bacterial taxa consisted of normal human skin bacteria, e.g. Anaerococcus spp., and environmentally derived taxa, e.g. Knoellia subterranea, many of which occurred in both male and female samples.

The biggest difference observed in male and female hairs in this study was the different proportions of the transient bacteria taxa. Almost twice as many transient bacterial taxa were present in female scalp hair compared to males.

This may be due to the greater frequency of females grooming / washing / dyeing / bleaching their hair in comparison to males.

This grooming practice may prevent the establishment of more stable bacterial colonies in favor of less stable (transient) bacterial colonies. Regardless of the reasons for this discrepancy, this observation cannot be considered significant with respect to forensic research.

Conclusion

Hair has multiple applications in forensic field as it is also useful in forensic toxicology, forensic chemistry, clinical toxicology, DNA analysis, etc.

The bacterial community that lives on a person's pubic hair can be analysed for microbial "features" that can be traced in a sexual assault case.

An alternative approach to identify the culprit by hair left at the crime scene could be through the detection of same microbial "signature".

Experts found that early discoveries showed that hair bacterial assessment particularly had major potential for forensic investigations, and found that the microbiota of human pubic hair appears to be transmitted during sexual intercourse has potential for forensic investigations and Medical expertise in sexual assault cases.

Written by: Tanu Sharma