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Year : 2017  |  Volume : 35  |  Issue : 4  |  Page : 443--444

Our microbial signatures

Prabha Desikan 
 Bhopal Memorial Hospital and Research Centre, Bhopal, Madhya Pradesh, India

Correspondence Address:
Prabha Desikan
Bhopal Memorial Hospital and Research Centre, Bhopal, Madhya Pradesh

How to cite this article:
Desikan P. Our microbial signatures.Indian J Med Microbiol 2017;35:443-444

How to cite this URL:
Desikan P. Our microbial signatures. Indian J Med Microbiol [serial online] 2017 [cited 2020 Jul 9 ];35:443-444
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Microbes in, and on, the healthy human body are known to outnumber the human cells by a ratio of 10:1. This probably makes us more microbial than human. Much interest has, therefore, been generated in the role of our microbiomes in health and disease. This interest led to the initiation of the human microbiome project (HMP). The HMP attempts to characterise the normal human microbiota and analyse their possible role in the maintenance of health and susceptibility to disease.[1] The HMP Data Analysis and Coordinating Center Data Portal is a curated portal, which provides access to various human microbial datasets.[2] These datasets have been used in various studies examining the influence of specific microbiomes on a range of scenarios from obesity to circadian rhythms.[3],[4] In contrast to host genomics, examination of the host microbiome allows for not only the detection and risk stratification of individuals at risk for disease but also their comprehensive follow-up and re-evaluation.

Surveys of the human microbiome using metagenomic codes have shown a strong variation in the microbial community composition between different individuals.[5] Some of these variations have been found to be stable over a period. Follow-up studies on individuals found that approximately 80% of individuals could be identified based on their gut microbiome for up to 1 year. These findings have fuelled speculation that individuals might have unique microbial 'fingerprints' that could distinguish them from other individuals.

Humans disperse microbes from their microbiome to the environment through direct contact with skin or mucosal membranes, or by bioaerosol particle emission through breath, skin, clothing, hair, etc., or through bacteria-laden dust particles.[6] Humans are known to shed approximately 30 million bacterial cells into their vicinity every hour.[7] While this is a documented mechanism of transmission of infection from one individual to another, it also results in an individual emitting a 'personal cloud' of microbes. People can leave behind a distinctive collection of microbes, based on their microbiome, in a built environment that they have inhabited. It is possible that this could be traced back to those individuals who had occupied that environment. Microbes shed by the occupants of a new house can be detected within a few days of their occupying the house.[8] This indicates the magnitude of the flux of microbes between humans and their built environment. Recently, emitted particles from humans may contain a distinctive bacterial pool that may collect in the built environment and get resuspended with dust particles. In this way, individual humans may actually, unknowingly, 'mark their territory,' quite like animals in the wild. Like this, new occupants of a house may 'mark' their new home as their own.

It is also possible to distinguish between the personal microbial contribution of different individuals within a built environment.[6] Such identifiability of individuals based on their microbial contribution in a built environment clearly has forensic applications. Microbial contributions through direct contact within a built environment last for long periods. In contrast, microbial contributions through bioaerosols would be more ephemeral, and may even get eliminated as a result of air flow of sufficient velocity. In such cases, forensic applications of microbiome profiles may require the use of microbial profiles from other environments, such as public spaces or spaces with a significant microbial input from environmental sources. Unfortunately, datasets on microbial profiles of environmental sources are currently not available.

While it is possible for an individual to shed a distinctive collection of microbial cells into a built environment, it is also possible for an individual to pick up a distinctive microbial assemblage from the environment or another individual. Such microbial profiles may be indicative of interaction with another individual or an individual's past presence in a specific environment. Given this possibility, it would be possible to link one individual to another as having cohabited that specific built environment. For example, the microbial community found on an individual's fingertips (microbial fingerprint) can be traced back to a keyboard, or even a mobile phone. Thus, the computer keyboard, mobile, and even keys, used by a person can be identified based on the microbial profile, which, essentially is equivalent to a microbial signature unique to an individual.[9],[10]

Other forensic applications of microbial signatures include prediction of body fluid type from microbial signatures found at the site of crime. It may be possible to determine the type of body fluid, and link to the human source of the body fluid from the microbial signature patterns found.[11] Interestingly, the dissimilarities in the constitution and composition of the microbiome may offer useful data which could also be utilised for criminal investigation purposes. Host lifestyle patterns, such as diet, occupation, travel, and drug use, can influence the composition and structure of a microbiome. This suggests that profiling the microbial signature of the human body could also help to provide information about an individual's lifestyle [12],[13] which, in turn, could offer additional evidence for forensic investigations.

With availability of automation for microbiome analysis, longitudinal microbiome-based follow-up of diseases and scenarios may become accessible and cost-effective even at local community settings. However, on a note of caution, since microbial compositions may change due to environmental factors and over time, they cannot be definitively equated with the host genome profile. While human microbial fingerprinting cannot replace traditional host genomic DNA profiling techniques, it could help augment the existing trace evidence options that can be made available for forensic investigations. This will require substantial investment in terms of standardisation and implementation of microbiome profiling techniques. It will also require the development of such technologies that can get automated or drastically reduce the turnaround time for microbiome profiling.

As an afterthought, humans are innately colonisers. Many intrepid adventurers have discovered and colonised various parts of the globe, leading to utilisation of newer reserves of resources. Having populated worldwide, space is now the next frontier. However, it appears that our enterprising microbes may have beaten us to it, having piggybacked on astronauts. Results of a study carried out on the international space station provide strong evidence that specific human skin-associated microorganisms make a substantial contribution to the microbiome in the space station.[14] Our astronauts may have left their microbial signatures in space for posterity. Would that be forensics for the future?


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