Scientists have successfully cultivated viruses from 700-year-old human feces found in ancient latrines. The closed barrels used as toilets dated back to the 1300s, and were uncovered in Belgium in 1996, during an urban development project. The barrels were found intact, suggesting that the fecal samples were protected from contamination during their internment. Measures were taken to prevent contamination of the samples in the transport from site to lab. Findings by the researchers were published in Applied and Environmental Microbiology.
The scientists found antibiotic resistance genes in the viruses cultivated from the fossilized fecal samples (called coprolites) in the ancient latrines, although the fecal samples predate the use of antibiotics by hundreds of years. These particular viruses are called phages, which is the term for viruses that infect bacteria rather than plants or animals. The phages bestow their antibiotic resistance genes on the bacteria in the process of infecting them.
Although at first one might be surprised to learn that viruses that existed years before the development of antibiotics, a look into the history of antibiotics offers an explanation. In 1871, Joseph Lister became interested in the fact that urine contaminated by mold would not grow bacteria. In 1928, Sir Alexander Fleming demonstrated the antibacterial properties of the mold Penicillium notatum. The point is, mold with antibacterial properties have been around a lot longer than the antibiotics made from them by humans.
It is now possible to look at the genetic sequence of a microbe and quickly compare it to the genetic sequences of other microbes. This information can be used to get a sense of how closely the microbes are related, and how long ago, in evolutionary terms, they started to grow apart. DNA taken from the viruses cultivated from the ancient latrines showed homologies (i.e., similarities) to phages commonly found in modern stools and soil. Christelle Desnues, a French researcher, and one of the authors of the study, noted that although the phages from the 700-year-old fecal samples were different from phages found in the feces of today’s humans, the ancient phage appeared to perform the same function as their modern counterparts.
To an evolutionary microbiologist, this suggests that despite changes in diet and the passage of time, the human gastrointestinal tract still requires the presence of “helpful” bacteria living harmlessly in the gut. These bacteria, in turn, require the antibiotice resistance genes conferred by the phages that infect them in order to continue living in human intestines. This also suggests that viruses may still be essential to human metabolism, and that this function has remained largely unchanged since at least the Middle Ages. If they had at some point ceased to be helpful, they would likely have died out over the passage of time, according to the rules of evolutionary biology.
Future work by the research team includes further studies of the ancient fecal samples, including an analysis of the fungi and parasites found in them. Their findings will contribute to ongoing work by historians, anthropologists, microbiologists and evolutionary biologists.
Although digging around in human feces from medieval latrines to cultivate viruses sounds like the kind of icky thing that only microbiologists would enjoy, the truth is that such studies produce interesting information and deepen our understanding of the relationship of human to microbe.
By Laura Prendergast