For the first time, researchers have reconstructed the DNA of an ancient strain of E. coli, according to a new study published in the journal Communications Biology.
To find the bacterium, the team turned to the mummified remains of a group of Italian nobles originally recovered in Naples in 1983. Per a statement from McMaster University, the team focused on one of them: a man named Giovanni d’Avalos, who died in 1586 at the age of 48, likely from chronic gallbladder inflammation due to gallstones.
Originally, researchers could only guess that d’Avalos carried E. coli, as the bacterium does not leave obvious signs of its presence.
“When we were examining these remains, there was no evidence to say this man had E. coli,” says George Long, lead author and a graduate student of bioinformatics at McMaster University, in the statement. “Unlike an infection like smallpox, there are no physiological indicators.”
But by examining the mummy’s gallbladder, the team was able to detect what they call an opportunistic pathogen—that is, a pathogen that likely won’t cause disease in a healthy host, but that can cause disease in a host with a weakened immune system.
Using fragments from a gallstone, the team identified the E. coli and reconstructed its genome. As it happens, the ancient strain is quite similar to a strain that exists today.
These days, E. coli outbreaks are reported and contained as part of standard public health practices, often leading to product recalls and new food handling regulations. Only a few strains are known to cause illness, which in most cases amounts to a bad bout of diarrhea. In some cases, though, E. coli can cause serious illnesses like hemolytic uremic syndrome, which can lead to kidney failure and death.
However, even though the bacterium has been around for quite some time, little is known about its history. While scientists have studied other ancient bacteria on many occasions, they often focus on “historically significant mortality events” like the Black Death, per the study.
“A strict focus on pandemic-causing pathogens as the sole narrative of mass mortality in our past misses the large burden that stems from opportunistic [pathogens] driven by the stress of lives lived,” says Hendrik Poinar, evolutionary geneticist and director of McMaster’s Ancient DNA Centre, in the statement.
By studying ancient strains of E. coli, the researchers say, we can learn more about its evolution. Today, for instance, some strains of E. coli are becoming increasingly resistant to antibiotics. Long hopes that the team’s work will help future researchers exploring how other “hidden pathogens” have evolved.