Scientists suggest that New York City's subway is infested with bits of Bubonic plague bacteria and mystery DNA.

The NYC subway is considered the lifeline of the city, without which the daily routine of millions of commuters would be disrupted.

Most of the microbes found in the subway system are harmless to humans. However, researchers at the Weill Cornell Medical College conducted investigations of the NYC subway microbes and found that some of them can cause disease and are resistant to drugs. The researchers also collected DNA fragments that are associated with the Bubonic plague and anthrax.

Dr. Christopher E. Mason, an assistant professor in the Weill Cornell's Department of Physiology and Biophysics, who is also the senior investigator of the study, believes that it is possible to create a pathogen map, or PathoMap, of the city that includes the subway. The PathoMap will help health-care departments accurately assess long-term disease surveillance in the city.

The researchers took bacteria samples from various locations and objects in the subway system, such as trash bins, ticket kiosks, benches, railings and more.

Thousands of microbes were discovered in the process. While not all bacteria are dangerous to humans, the scientists found 12 percent that could still cause diseases in humans; these diseases were present in 27 percent of the total fragments collected as part of the study.

"Our data show evidence that most bacteria in these densely populated, highly trafficked transit areas are neutral to human health, and much of it is commonly found on the skin or in the gastrointestinal tract," Mason said. "These bacteria may even be helpful, since they can out-compete any dangerous bacteria."

Two samples were found to have DNA fragments of anthrax and three samples had a plasmid associated with the Bubonic plague.

The existence of the DNA fragments does not mean that they are still alive. Culture experiments revealed no sign of them being alive. The study also revealed that about 50 percent of the DNA found on the subway's surfaces did not match any known organism.

"Despite finding traces of pathogenic microbes, their presence isn't substantial enough to pose a threat to human health," said Mason. "The presence of these microbes and the lack of reported medical cases is truly a testament to our body's immune system and our innate ability to continuously adapt to our environment."

However, wider testing is required to assess the bacteria.

While several types of bacteria are present in the NYC subway, not a single case of plague has been reported in the city since 2013, the same year the PathoMap project started.

The study "Geospatial Resolution of Human and Bacterial Diversity with City-Scale Metagenomics" is detailed in the journal Cell Systems.