Which Bacteria Decompose Your Bloated Body?

This article was originally posted on RealClearScience.

Americans insist on experiencing “death with dignity.” The reality, however, is that death is not even remotely a dignified process, particularly if nature is allowed to take its course unimpeded. Once you shuffle off this mortal coil, your body goes through a series of drastic changes, each stage more ghastly than the last.

Immediately after death, since your muscles relax, you may urinate and defecate on yourself. After about three hours, your muscles undergo rigor mortis, where they become very stiff. After about 72 hours, the stiffness subsides, but your tissues start to decay. As bacteria decompose your body, they release awful smelling gases that cause it to bloat, which in turn forces a sickly green ooze of fluids out of your body. If you’re really lucky, your rotting corpse will attract flies, providing sustenance to several generations of maggots.

It is the bloated stage that has attracted the attention of researchers from Texas. They wanted to examine the kinds of bacteria that are present during this particular stage of decomposition.

The scientists placed two dead guys on their backs outside. The first man (#016) was diabetic and died from myocardial infarction (heart attack), and the second man (#006) died of carbon monoxide poisoning. Both bodies had been stored in a freezer for an extended period of time before being brought to an outdoor facility to undergo what had to have been the most interesting experiment of their existence.

The researchers sampled various parts of the corpses for microbes at the beginning and at the end of the bloated stage. Corpse #006 was placed outside in September 2011, and his bloated stage lasted seven days. Corpse #016 was placed outside in November 2011, and his bloated stage lasted 14 days. They then sequenced 16S rRNA genes to identify the microbes present. What did they find? Well, it’s hard to draw any conclusions because the study was rather poorly designed. (For the sake of brevity, we show results below only for corpse #006.)

Only the “mouth scrape” had before (pre-bloat) and after (end-bloat) samples. For corpse #006, the pre-bloat mouth scrape showed almost exclusively Proteobacteria (specifically, Pseudomonas, an aerobic bacterium). After seven days, the end-bloat mouth scrape showed a substantial shift: The Proteobacteria had been replaced by Firmicutes (specifically, Peptoniphilus and Clostridium, both anaerobic). This supports other research which shows that the microbiome shifts from aerobic to anaerobic during the process of decomposition.

However, the other corpse had a very different microbiome, and there was no obvious shift from aerobic to anaerobic bacteria in the mouth scrape.

The authors can be excused for using only two corpses; indeed, dead human bodies are not the easiest things to obtain. But why the authors chose not to select more body sites for before-and-after sampling is puzzling. Also, the authors did not sample bacteria from the environment, which surely had an impact on decomposition. Most importantly, the authors did not attempt to control any conditions, whatsoever. One body was exposed to September weather, while the other was exposed to November weather. It would have been more informative to place the corpses side-by-side, or to perhaps have placed one corpse in a sterile or climate-controlled environment.

As such, this experiment wasted two perfectly good corpses.

“Exploratory” studies like this one can yield very interesting and informative data, but only if they are designed properly. Therefore, it is difficult to see how this paper contributes anything meaningful to the literature. PLoS ONE would have been well-advised to reject it.

Source:  Hyde ER, Haarmann DP, Lynne AM, Bucheli SR, Petrosino JF (2013). “The Living Dead: Bacterial Community Structure of a Cadaver at the Onset and End of the Bloat Stage of Decomposition.” PLoS ONE8(10): e77733. doi:10.1371/journal.pone.0077733