If you're among the billions of people who use public transport on a regular basis, you share much more than a commute with your passengers, suggests a new study published in Cell on Tuesday , They also share and trade the teeming microbes that call our bodies home.
Researchers in Hong Kong – home to a public transportation system serving 5 million commuters every day – recruited volunteers for a unique experiment. Over the course of several days, volunteers were asked to drive one of eight subway lines on the Hong Kong Mass Transit Railway system during morning and evening rush hours. Before embarking, they washed their hands and, when they were on board, used the handrails extensively. After spending 30 minutes on the train, they undressed and were dabbed by researchers' palms.
Through these palm samples, the researchers were able to track changes in the microbial community or microbiome of various subway lines as day went along. What they found, according to author Gianni Panagiotou, a systems biologist at the University of Hong Kong, was fascinating and a little scary.
"In the morning, each line has its own microbial properties, which to a large extent was the case, reflecting the characteristics of the city it is going through." For example, the subway line that runs along the coastline became mainly populated with aquatic bacterial species, "Panagiotou told Gizmodo by email. "Throughout the day, as more and more people used the Metro, the microbial community has become more and more similar, dominated by the commensal bacteria of the human skin," means bacteria that typically live on human skin.
It is not the first time that scientists have uncovered the bacterial subsoil of mass transit. Recent studies have also examined the microbiota of Boston and New York subways, relying on samples taken from tensile surfaces or surrounding indoor air. But Panagiotous's team, working with architect Chris Webster, also at the University of Hong Kong, wanted to develop a better sense of how the changing environment of a city and the people living in it can influence the microbiome.
Like previous studies, they found that most beetles that populated the subway were completely harmless, whether they came from our skin or elsewhere. But the day-night comparison also showed how efficiently the underground can spread bacterial strains known to cause disease, as well as replaceable genes that allow bacteria to withstand the antibiotics used in humans.
In the morning, the team found that only a few lines contained these antibiotic resistance genes or ARGs, but by night, they all did.
"The idea for these projects is not to scare people, it's more recognizable that we're constantly exposed to different bacteria," said Panagiotou. "And also to accept that the way we shape our cities can have a significant impact on the type of bacteria we will encounter."
For example, his team did not find that less-utilized trains were associated with fewer germs than antibiotic resistance genes until the evening rush hour, which means that the (relatively low) risk of exposure to potentially dangerous microscopic threats is truly unavoidable. But one of Hong Kong's lines is currently crossing into a Chinese city. And this line had noticeably higher levels of ARGs than the rest.
While this finding does not necessarily mean anything, Panagiotou noted that China is much more liberal about its antibiotic use than Hong Kong. China is the leading consumer and producer of antibiotics in the world, resulting in a much higher proportion of residual antibiotics in the environment. As a result, experts have already discovered signs of a growing antibiotic resistance crisis erupting from the country.
"Everything we do, every choice we make, leaves its mark on the microscopic world that surrounds us," Panagiotou
Although Panagiotou is troubling in many ways given the continuing rise in antibiotic resistance, he said, that its results also indicate that we can take positive steps to fight it.
Hong Kong points out The SARS virus, which killed nearly 300 people in Hong Kong in its first documented outbreak in 2003, has led to sustained cultural and public health changes. According to Panagiotou, people still wear masks and are wary of spreading germs, and Hong Kong has many public hand washing and antiseptic stations. MTR Corporation, the company that runs the transport system, carefully disinfects and coats the trains with antibacterial agents – a policy that could explain why the total amount of bacteria found in the study was relatively low. Similar measures could be implemented in other major cities, especially during the flu season.
"If this policy has not been implemented," Panagiotou said, "I would expect to see much higher risks."