Monday Micro – the microbiome of death!

By Siouxsie Wiles 01/09/2014 3


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With microbiome analysis being all the rage at the moment, it was only a matter of time before someone decided to profile the microbes present in human cadavers. Which is what Ismail Can and colleagues have just published in the Journal of Microbiological Methods (alas, it’ll cost you almost $40 to read their article if you don’t have a subscription).

The researchers wanted to know what happens to our microbiome – the microbes that live in and on us, and outnumber our own cells by 10 to 1 – after we die. What happens to the human body after death is pretty well documented. When the heart stops pumping, the lack of oxygen causes our cells to become hypoxic which triggers the release of enzymes which in turn cause our cells to lyse. This cell lysis releases nutrients into the surrounding tissues, allowing any microbes present to feast and multiply. The lack of oxygen also causes the microbes to shift from aerobic to anaerobic fermentation resulting in the build-up and release of gases, including hydrogen sulphide and methane.

Ismail and colleagues collected samples from the blood, brain, heart, liver and spleen of 11 corpses with known times of death, ranging from 20 hours to 10 days. The organs they chose are ones which would not have any microbes present in a normal healthy person. They then isolated and amplified microbial DNA from the samples and sent them off to be sequenced, to find out which microbes were present.

What the researchers wanted to know was whether there would be a specific pattern and timing for when particular classes of microbes turn up in the different organs after death. If this happens, then it may be that the microbes could be used to indicate how much time has passed since the person died. The authors coined a new phrase for the microbiome of cadavers, the thanatomicrobiome. In Greek mythology, Thanatos is the god of death.

So will we soon be hearing talk of thanatomicrobiomes on CSI? Probably not. The results did show some difference between the bacteria present and the age of the corpse, with the organs of the newest corpses having bacteria such Streptococcus, Lactobacillus and Escherichia coli present (these are bacteria able to mop up any oxygen left in the tissues after death), and the organs of older corpses more likely to contain bacteria that live in the absence of oxygen, like species of Clostridium. But there was a lot of variation between the corpses, and no pattern to which microbes where found in a particular organ. Looks like those CSI teams may have to stick to using insect larvae to date their cadavers for now.

H/T to Kent Atkinson for suggesting this paper for a Monday Micro post

Reference:
Can I, Javan GT, Pozhitkov AE, Noble PA (2014). Distinctive thanatomicrobiome signatures found in the blood and internal organs of humans. J Microbiol Methods. 106C:1-7. doi: 10.1016/j.mimet.2014.07.026.


3 Responses to “Monday Micro – the microbiome of death!”

  • Could you expand on this bit:
    “The organs they chose are ones which would not have any microbes present in a normal healthy person.”

    The brain I understand because of the BBB, but why might we expect the others to be sterile?
    I’m given to understand that where-ever we have actually looked closely we have found micro-organisms. Is the assumption that our immune system should be mopping them up or are there particular reasons independent of that that they would be microbe free?

    • The assumption is that those organs are kept microbe free by the immune system in healthy people. They certainly found most of them to be microbe free (or at least at undetectable levels) in the 20h corpses. But its a good point and I’ll see if I can find some paper on it.