A grave understanding of microbes.

Happy Halloween week!

During this spooky time of the year, you may come in contact with various creatures of the supernatural; common encounters include witches, werewolves, ghouls and – a personal favorite of mine – zombies.

Continuing my series of posts dedicated to the zombie apocalypse, here I will discuss another important topic concerning zombies: decomposition.

  Greg Nicotero's 'Bicycle Girl'  from the first episode of  AMC's the Walking Dead . Click the link for a behind the scenes video or check out great examples of decomposition Sunday nights at 9 PM EST.

 Greg Nicotero's 'Bicycle Girl' from the first episode of AMC's the Walking Dead. Click the link for a behind the scenes video or check out great examples of decomposition Sunday nights at 9 PM EST.

What is ‘decomposition’?

Decomposition is the process by which organic matter is broken down into smaller pieces. In more gruesome terms: we rot. Rot gives zombies that certain visual appeal we all know and love.

And the smell.

Like it or not, our humans lives will inevitably come to an end and the process of decomposition – and perhaps zombification – will take over.

How quickly does decomposition take over?

In as little as 4 minutes.


What exactly is ‘death’, anyways?

Technically, the exact definition of death according to Wikipedia.org is ‘the cessation of all biological functions that sustain a living organism’, which in this case is us.

We may stop breathing and our heart may stop beating but does that mean all the cells in our body die in the same moment we do? Not exactly.

With no lung function and blood flow, oxygen and pH levels drop in the body while carbon dioxide and waste levels raise, poisoning our cells. The functions of our cells, normally controlled by enzymatic proteins, go haywire and our cells start to digest themselves.


This digestion results in the dramatic release their enriched guts in a process referred to as autolysis.

Microbes do not leave a sinking ship, they eat it.

We are all covered in microbes, internally and externally. In fact, microbial cells outnumber our own human cells ten to one

As we die and these microbes lose their home, they do not simply die with our body; they take advantage of our unfortunate situation and eat the nutrients being dumped by our cells.

These opportunistic microbes include various types of bacteria, fungi and protozoa. Many of which were on your body during your life and time of death along with some others that wandered in from the outside.

You can easily recognize this stage of the decomposition based on what the microbes produce as they eat your remains: gas.

As your soft tissue is broken down into smaller building blocks and gases build up, your body begins to bloat. Hence, bloat has become the name that commonly represents the second stage of decomposition more formerly known as putrefaction

As putrefaction proceeds, microbes flourish and insects may also join the scene to produce maggots. The process then begins to enter the decay stage, which is characterized by the greatest loss in body mass. The byproducts of this breakdown begins to leech into the environment and can even cause death to surrounding vegetation.

After the dust has settled and microbes move on, all that is left is the final stage: dry remains. 

Timecourse of a pig carcass illustrating the stages of decomposition analogous to human decomposition. Image credit: Hbreton19 at wikipedia.

Beyond the grave: what microbes can tell us.

Forensic science exists to identify and interpret physical evidence related to someone’s death. In many crimes surrounding a body, the process of decomposition can elucidate a very crucial piece of evidence: the time of death or postmortem interval (PMI).

Classic parameters used to determine PMI include the development rate of fly larvae and other insects as well as changes in the biochemistry of the soil surrounding the body.

However, decomposition is a messy process.

Soil can be highly variable from site to site and some environments harbor lots of flies while others have none. As a result, these parameters tend to be less reliable since they depend on external factors outside the body.

Enter forensic microbiology.

Forensics at work with the West Midlands Police.

Forensics at work with the West Midlands Police.


As I said before, we harbor ten times more microbes than human cells in and on our body.

Using this information, researchers at the University of Colorado in Boulder have developed a way to look for microbial signatures in our bodies as a “microbial clock” to more accurate determine PMI.

Since the decay process follows distinct changes in chemistry as time progresses, the researchers found that the microbial communities of decomposing mice bodies followed dramatic, repeatable patterns of change.

What else can microbial forensics tell us?

PMI may not be the only useful piece of information microbes can share: the same research group at UC Boulder also demonstrated they could track a person around a room using the microbes found on their hands as a microbial fingerprint.

Combined, forensics may someday be able to use microbes in many aspects of criminal investigations to overcome the shortcomings of current techniques.

And remember, when you see that zombie during Halloween weekend, take a swab sample and compliment him on his nice putrefaction.

Stay hungry!