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Horror film or new episode of CSI: your post-mortem microbiome

If you are a regular reader of this blog, you would be aware of the amazing range of things your gut microbiome can affect. From heart health to mood, we think the bacteria living in your intestine might play an important role. However, that is all while you are alive. Have you ever thought about what happens to the bacteria living inside you when you die? And could it actually be useful?

The "thanatomicrobiome"

When you are alive, your immune system, and other mechanisms, ensure that bacteria in your body are kept to specific areas (for example in your intestine, but not in your blood). However, soon after you die (as soon as a few minutes!), these safeguards breakdown, and dying cells start to leak nutrients bacteria can use as food. This causes huge amounts of bacterial growth, and eventual takeover of the body. These bacteria are called the ‘thanatomicrobiome’. Researchers have used innovative methods to understand what types of bacteria grow most after death, and have found some surprising things. It was originally thought that there would be a common pattern between people in microbial growth, with certain types of bacteria flourishing in some parts of the body, and other bacteria being more common in other parts. However, it was actually found that the thanatomicrobiome is more similar across organs and blood from the same person. This was a bit different to another study, which looked at growth of bacteria in the mouth after death. As expected, soon after death, bacteria we know are usually found in the mouth were most common. However, shortly after, bacteria usually found in the gut started to take over. Then after a while, when all the oxygen in the body had been used up, other bacteria called anaerobic Clostridiales grew more.

Calculating time of death?

While knowing what bacteria grow after death is interesting, it wasn’t thought to be very useful for us in the land of the living. However, we soon learned that different types of bacteria were more often found in people who had recently died (i.e. people who had a short post-mortem interval, or PMI), than people with a long PMI. We have traditionally found it quite difficult to determine time of death in some cases, which can be very important in the instance of crimes. Traditional measures such as body temperature, settling of blood and stiffness can be affected by weather conditions and even clothing. New research used special mathematical models and machine learning to understand bacterial growth from the skin and surrounding soil and its correlation to time of death. Of course, there are lots of practicalities to consider whether it is feasible to use bacterial growth as a measure of PMI, and this is an issue researchers are trying to understand now.

New research suggests that the microbiome may be a useful tool in determining time of death.

Listen to this short podcast about using a ‘body farm’ to measure the PMI using bacteria.

Understanding health of communities - can we predict disease?

Another use for the post-mortem microbiome might be as a health surveillance tool. One study found evidence that people who had heart disease during life, had less type of bacteria after death. Additionally, the postmortem microbiome reflected a range of living conditions and lifestyles. The authors suggested that routinely taking bacterial samples from people after death could lead to lots of new understanding about our microbiome when we are alive. If the microbiome could be used for health surveillance, we may overcome issues we have with linking disease and bacteria in life (for example problems with taking samples from people’s insides). This still needs a lot more research to become reality, but it could be an interesting way to predict disease via microbial analysis.

So with our microbes constantly with us, it seems we are never alone in life, or death.

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