Microbes discovered that could help police pinpoint time of death, scientists say

Despite what television crime shows may suggest it is notoriously tricky to estimate time of death once rigor mortis has subsided – ASHLEY COOPER/THE IMAGE BANK RF

Death microbes which cause the human body to rot have been identified by scientists in a breakthrough that could help police pinpoint the time of death in crime scenes.

Although crime dramas on television often show pathologists accurately predicting a time of death, it is actually notoriously tricky to estimate once rigor mortis has subsided, which happens within about 24 hours.

To find out if changes in the body could help, the American National Institute of Justice (NIJ) funded a study in which 36 human corpses were allowed to decompose in different climates and seasons in the United States.

Scientists from Colorado University then took skin and soil samples over a 21-day period and found that about 20 species of bacteria and fungi turned up “like clockwork” at certain times in the process.

Microbes present included the bacterium, acinetobacter which causes urinary infections and pneumonia, and wohlfahrtiimonas which is responsible for blood infections.

The team believe that the bugs are being brought via insects which infest the body after death, rather than coming from the gut of the dead person.

“It’s really cool that there are these microbes that always show up to decompose remains,” said Prof Jessica Metcalf, of Colorado University, the senior author on the study.

‘Regardless of variables’

“We see similar microbes arrive at similar times during decomposition, regardless of any number of outdoor variables you can think of. The waves of microbes are clock-like.

“We all suspected that our own microbes would betray us after death, and they still may, but the specialist decomposers, those microbes that seem really adapted for this process, appear to come in on the insects, not from our bodies or from the soils.”

Researchers believe that in future, police will be able to sample the microbiome of a crime scene to gauge how long a dead body has been at the location.

The team discovered that the same set of about 20 species were present regardless of the type of soil or climate, suggesting they play a universal role in decomposition.

Using machine learning, experts have also built a computer program that can determine the time of death by looking at the quantities of the species, which ebb and flow.

“When you’re talking about investigating death scenes, there are very few types of physical evidence you can guarantee will be present at every scene,” said David Carter, professor of forensic sciences at Chaminade University of Honolulu, who helped develop the program.

“You never know if there will be fingerprints, or bloodstains or camera footage. But the microbes will always be there.”

‘Promising results’

Nancy La Vigne, director of the National Institute of Justice said. “One of the principal questions of any death investigation is ‘when did this person die?’

“This continuing line of NIJ-funded research is showing promising results for predicting time of death of human remains, aiding in identification of the deceased, determining potential suspects and confirmation or refutation of alibis.”

The team also attempted to determine where the microbial community came from and discovered that none of the species were present in soil microbiome databases or catalogues of human skin and gut microbiomes.

Instead it appears that insects are bringing them to the body after death.

The research was published in the journal Nature Microbiology.

%n

Discover Telegraph Wine Cellar’s new wine club. Enjoy expertly chosen bottles at exclusive member prices. Plus, free delivery on every order.