The long lens of the law

We already use microbiology routinely in forensic pathology for identifying potential organisms which could be causing a disease or infecting a wound.  However work in recent years looks like it might be adding some more roles for the microbiologist in forensic investigations.

Bacteria are grown in labs to allow identification of the species.

Bacteria are grown in labs to allow identification of the species (Image from Wikimedia)

Forensic microbiology is an exciting area of research at the moment, including uses in forensic identification, tracking the interaction of people with their environment, and even deducing time since death in cadavers.

The bacteria which live on healthy individuals is called the human microbiome, and is similar between all humans.  However, it is the differences between individuals which has attracted the attention of some pioneering microbiologists.  The Human Microbiome Project is attempting to answer some basic questions about our microbiome (Blaser 2010):

  1. Which species of microbe inhabit humans?
  2. What are the microbes doing?
  3. How is the immune system responding to these microbes?
  4. What are the forces maintaining the balance between microbe and human?
  5. What are the unique characteristics between humans?

A group from Washington University School of Medicine (Fierer et al 2010) has shown that you can identify individuals based on the unique population of bacteria inhabiting their skin.  Not only that, but you can compare the population on their skin to the population on an inanimate object, such as your computer keyboard and mouse to identify who used it!

E coli

E coli (Image from Wikimedia)

Another group has shown that cell phones share the microbiome of their human owners (Meadow et al 2014) and Simon Lax (2014 and 2015) has shown you can link the bacterial population on people’s shoes  and the floor to work out where people have been…

Particularly exciting to pathologists is the potential to use the change in bacterial population on a dead body over time to estimate the time since death.  More work is required in this area, but the results from Jessica Metcalf at the University of Colorado at Boulder looking at mice are promising.

Of course, there are limitations to these applications which need more work, such as the effect of antibiotics and cleaning products which may be present in the person, cadaver or environment which could confuse results.

References and further reading:

Blaser MJ. Harnessing the power of the human microbiome. PNAS 2010;107:6125-6126.

Fierer N, Lauber CL, Zhou N, McDonald D, Costello EK, and Knight R. Forensic identification using skin bacterial communities. PNAS 2010;107:6477-6481.

Metcalf JL, Parfrey LW, Gonzalez A, et al. A microbial clock provides an accurate estimate of the postmortem interval in a mouse model system. eLife 2013;2:e01104.

Meadow JF, Altrichter AE, and Green JL. Mobile phones carry the personal microbiome of their owners. PeerJ 2014;2:e447.

Lax S, Smith DP, Hampton-Marcell J, et al. Longitudinal analysis of microbial interaction between humans and the indoor environment. Science 2014;345:1048-1052.

Lax S, Hampton-Marcell JT, Gibbons SM, et al. Forensic analysis of the microbiome of phones and shoes. Microbiome 2015;3:21.