The archaeologist Henrike Kiesewetter of Germany’s Tüebingen University was examining the skeleton of a 30-year-old woman unearthed near the ruins of the ancient city of Troy, when she noticed two calcified strawberry-sized nodules at the base of the chest, just below the ribs. At first glance, the nodules appeared similar to those caused by tuberculosis. But when Kiesewetter sent the nodules to Caitlin Pepperell, a professor of medicine and microbiology at the University of Wisconsin-Madison and an expert on the evolution of pathogens, and Pepperell performed DNA analysis along with elemental and microscopic analyses, the results showed they weren’t due to tuberculosis, or to urinary or kidney stones.
Intrigued, the researchers opened the cells and found well-preserved microfossils that closely resembled bacteria from the genus Staphylococcus, which includes the common, highly pathogenic (or disease-causing) bacterium S. aureus, among many other species. They sent them on to Hendrick Poinar of McMaster University in Ontario, Canada, whose laboratory specializes in ancient DNA. “Amazingly, these samples yielded enough DNA to fully reconstruct the genomes of two species of bacteria, Staphylococcus saprophyticus and Gardnerella vaginalis, which infected the woman and likely led to her death,” Poinar said in a press release from the University of Wisconsin-Madison.
Poinar and Pepperell led the team of researchers in producing a “portrait” of Staphylococcus saprophyticus, the ancient infection that killed the woman. When typically working with ancient DNA, scientists can hope for less than 1 percent of the target organism to be preserved over time. But in this case, as Pepperell put it, “Calcification made little tiny suitcases of DNA and transported it across an 800-year timespan.” Somewhere between 31 and 58 percent of the preserved DNA came from the bacteria that caused the woman’s infection, allowing Pepperell and her colleagues to extract a staggering amount of information. The researchers’ creation of a genetic blueprint of Staphylococcus saprophyticus, Pepperell said, meant it would join “a pretty short list of ancient bacteria—cholera, tuberculosis, leprosy, plague—for which we have DNA.”
The research team’s findings, published this week in the journal eLife, suggested that the woman died of chorioamnionitis, which is a bacterial infection of the placenta, amniotic fluid and membranes around the fetus. Alongside the woman’s own DNA and that of the bacteria causing her infection, the scientists also identified an ancient Y chromosome DNA, which likely belonged to a male fetus.
Though many women certainly died from complications of pregnancy and childbirth in ancient times, it is extremely rare to find a case of maternal sepsis in the fossil record. “There are no records for this anywhere,” Poinar said. “We have almost no evidence of what maternal health and death was like until now.”
The strain of the infection that killed the woman was different from the type that usually afflicts humans today; in fact, it was closer to modern strains found in livestock. As the historical record shows that people in Byzantine-era farming communities typically lived alongside their livestock, the researchers believe human infections at that time may have been caused by a bacteria pool that circulated relatively freely between humans, livestock and the environment.
The pregnant woman was not the only one who suffered the difficulties and indignities of life in her ancient agrarian community. “People were struggling with physical strains and infectious diseases and only a few lived beyond the age of 50,” Kiesewetter said of the other human remains found in the late Byzantine graveyard. “Many newborns did not survive infancy and almost all skeletons of children show signs of malnutrition and infection.”