An international team led by researchers from McMaster University in Canada, working in collaboration with Paris Cité University in France, identified and reconstructed the genome of the bacterium E. coli ancient, using fragments extracted from the gallstone of a 16th century mummy.
The discovery is published online in the journal Communications Biology.
E. coli is a major public health problem, causing significant death and morbidity, but is not a source of pandemics. It is known as a commensal, a bacterium that resides within us and can act as an opportunistic pathogen by infecting its host during times of stress, disease or immunodeficiency.
Its entire evolutionary history remains a mystery, including when it acquired new genes and antibiotic resistance, the researchers say, according to EurekAlert.
The genome of the ancient E. coli bacterium is useful in understanding the evolution of the bacterium
Unlike well-documented pandemics such as the Black Death, which persisted for centuries and killed up to 200 million people worldwide, there are no historical records of deaths caused by eaters such as E. colialthough the impact on human health and mortality was probably tremendous.
“A strict focus on pandemic-causing pathogens as the sole narrative of mass mortality in our past misses the great burden arising from opportunistic commensals driven by life stress,” says evolutionary geneticist Hendrik Poinar.
bacterium E. coli modern is commonly found in the intestines of healthy humans and animals. While most forms are harmless, some strains are responsible for serious, sometimes fatal outbreaks of food poisoning and bloodstream infections. The bacterium, which is hardy and adaptable, is recognized as particularly resistant to treatment.
The genome of the 400-year-old E. coli bacterium gives researchers a term of comparison with the modern bacterium to study how it has evolved and adapted since then.
The bacteria were “donated” by a mummy
The mummified remains used for this study came from a group of Italian noblemen whose well-preserved bodies were recovered from the Abbey of Saint Domenico Maggiore in Naples in 1983.
For the study, the researchers conducted a detailed analysis of one of the individuals, Giovani d’Avalos. This was a Neapolitan nobleman of the Renaissance period; he was 48 when he died in 1586 and was believed to have suffered from chronic inflammation of the gallbladder due to gallstones.
“When we examined these remains, there was no evidence that this man had E. coli. Unlike an infection like smallpox, there are no physiological indicators. Nobody knew what it was,” explains the study’s lead author George Long, a bioinformatics graduate student at McMaster, who conducted the analysis with co-lead author Jennifer Klunk, a former graduate student in the university’s Department of Anthropology.
A ubiquitous bacterium
The technological achievement is particularly remarkable because E. coli it is both complex and ubiquitous, living not only in soil but also in the human microbiome. The researchers had to painstakingly isolate fragments of the target bacteria that had been degraded by contamination from multiple sources. Scientists used the recovered material to reconstruct the genome.
“It was so exciting to be able to rebuild this E. coli ancient and to find that, although it is unique, it belongs to a phylogenetic lineage characteristic of human commensals, which still causes gallstones”, says Erick Denamur, leader of the French team that was involved in the characterization of the strain.
“We were able to identify what was an opportunistic pathogen, uncover genome functions, and provide guidelines to help researchers who might explore other hidden pathogens,” says Long.