Move over, "C.S.I."

Scientific sleuths at the University of Colorado are pursuing research that could provide criminal investigators one more way to determine approximate time of death, a tool they call the microbial clock.

The research is highlighted in just the most recent of more than a dozen papers authored or co-authored by CU researchers published in the past several years on human microbiomes, the estimated 100 trillion or so microbes that live on, and in, each one of us.

Jessica Metcalf, a senior research associate at CU's BioFrontiers Institute, is the lead author on a study determining that the microbial clock, essentially the fixed succession of bacterial changes that occur as bodies decay, could be an effective means in determining time of death.

And although Metcalf and her associates' preliminary work was done on mice, they are now moving into exploring its application to human cadavers.

A paper on the subject was published this week in the new online science and biomedical journal eLIFE. The study was funded by the National Institute of Justice.

"A fundamental question was whether microbes change in a consistent manner across replicates," Metcalf said. "That's what we would want to see if we were going to use microbes as a clock to estimate the time since death. A mouse model system allows you to do this under very controlled conditions."


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Using 40 dead mice, the researchers "destructively sampled" the microbial communities in each mouse, five at a time, at eight time points, over a period of 48 days. This included the stages of "freshly" dead, active decay and advanced decay.

"At each time point that we sampled, we saw similar microbiome patterns on the individual mice and similar biochemical changes in the grave soil," Laura Parfrey, a former CU postdoctoral fellow and now a faculty member at the University of British Columbia who is a microbial and eukaryotic expert, said in a news release.

"And although there were dramatic changes in the abundance and distribution of bacteria over the course of the study, we saw a surprising amount of consistency between individual mice microbes between the time points -- something we were hoping for."

Using high-technology gene sequencing on bacteria and microbial eukaryotic organisms such as nematodes, fungi and amoeba postmortem, the researchers were able to derive the approximate time of mouse death.

"What we found was that the change in the microbial community was so consistent that we were able to estimate its time since death to within three days," Metcalf said.

Researchers are now planning to apply the same science to DNA swabs from human cadavers at what is colloquially known as a "body farm" but more properly is known as the Southeast Texas Applied Forensic Science Facility, an outdoor human decomposition facility, utilizing the remains of those who have pledged their bodies to science.

Law enforcement investigators typically have other tools available for determining time of death, including body temperature, text and phone messaging records, even forensic entomology -- the study of the progress of insect life in a corpse.

"One of the advantages to this technique is that it may not have the same uncertainties as others," Metcalf said. "They can be used complementary to one another, to help narrow that window. ... This is another tool that could potentially help criminal investigators, specifically."

CU associate professor Rob Knight, senior author on the grant and principal investigator at CU's BioFrontiers Institute where the study took place, said, "This work shows that your microbiome is not just important while you're alive. It might also be important after you're dead."

Contact Camera Staff Writer Charlie Brennan at 303-473-1327 or brennanc@dailycamera.com.