Scientists Track How Antibiotic Resistant Microbes Can Hitch Rides on the Subway

A woman holds the hand of a young girl wearing a mask as they enter a subway station of Hong Kong on May 2, 2009. Research showed how microbes traveled though the Hong Kong subway system in a study published on Tuesday. PHILIPPE LOPEZ/AFP/Getty Images

Microbes live all around us. They thrive in our guts and propagate on our skin. They also ride the subway.

Some microbes can lead to illnesses like stomach bugs that are easily treated, but others are far worse. Antibiotic-resistant bacteria are so resilient they can sometimes kill their human hosts. This is why one team of scientists at the University of Hong Kong wanted to better understand how dangerous pathogens travel through cities and move through populations.

The researchers studied the metro rail system in Hong Kong, the perfect Petri dish in which to observe how microbes travel through an urban environment. They wanted to track the potential transmission of antibiotic resistant genes to reveal how urban design could influence microbial ecology and transmit disease. "With five million people riding the subway every day, the fingerprint of the whole city had to be there," Gianni Panagiotou, a systems biologist at the Hans Knoell Institute in Germany and the University of Hong Kong, said in a press release.

Commuters sit in a train on a platform inside the Central station in Hong Kong, on May 27, 2014. Research published on Tuesday tracked the transmission of microbes that are found on Hong Kong commuters’ skin. Brent Lewin/Bloomberg via Getty Images

There, Panagiotou and his team observed and cataloged the microbial populations passengers encounter on their daily commutes. Subway lines, it turns out, have distinct microbe populations during the morning commute, but by evening time, there was more of a mishmash of different microbes.

It also appeared antibiotic-resistant genes accumulated throughout the day. Different subway lines also have distinct bacterial ecology. The research also revealed that antibiotic-resistant bacteria appeared higher in lines closer to Shenzhen, a city on the Chinese mainland, where farmers are known to give their pigs feed laced with antibiotics. This is of concern since bacteria often spread these immunities to each other. The findings were published in the journal Cell Reports.

"The idea for this project is not to scare people, because what we observed was that higher traffic metro lines do not carry higher health risks, neither in terms of pathogens or in terms of antibiotic resistance genes," said Panagiotou. "We want to better understand how urban planning can impact the types of bacteria."

During the study, the researchers sent volunteers through the subway system for half an hour during both the morning and evening rush hours, taking cultures of the skin on their hands after each trip. The researchers investigated which bacteria were transferred to commuters' hands. Earlier studies in Boston and New York City subways have already evaluated the microbes that live on the train compartment surfaces themselves.

Metro employees on the Hong Kong rail system clean train surfaces that people touch throughout the day, but that doesn't seem to stop the flow of microbes transmitted on to human skin.

The majority of microbes transferred were relatively harmless bacteria that live on the skin, but some pathogens were discovered as well. There seemed to be less of a risk for morning commuters, with antibiotic resistant genes only detected on a few train lines. By the evening rush hour, antibiotic resistant genes could be traced in all of the subway lines.

These findings, the researchers hope, can influence urban planning and the ways that public transit systems are designed.

"Studies like ours investigating the microbial composition of train compartments may guide future public health strategies and public transit designs," Panagiotou said.