Last updated October 25, 2018 at 1:34 pm
Study shows they become one uniform group by day’s end.
Credit: iStock / Olaser
There’s more movement than you might imagine along Hong Kong’s 160 kilometres of subway.
Not only do nearly five million people use it to commute each day, some from as far away as the Chinese mainland, but many millions more microbes are moving in quite distinct ways.
A new study shows that while each subway line hosts a characteristic set of bacteria during morning rush hour, by evening they have joined into one uniform microbiome populating the entire system.
Systems biologist Gianni Panagiotou and architect Chris Webster wanted to learn how the geographical features of the different subway lines and their connectivity to urban streets and other public spaces affected the overall microbial composition of the subway. Then, they wanted to see if the microbiome itself would inherit the tidal effects of the traffic flow enough to vary over travelling time.
“With five million people riding the subway every day, the fingerprint of the whole city had to be there,” said Panagiotou, who spreads his time between the Hans Knoell Institute in Germany and the University of Hong Kong.
Skin on hands sampled
To simulate the average commuter experience, volunteers rode the subway for half an hour during the morning and evening rush hours, then the skin on their hands was sampled each time.
Because the skin is a major biointerface critical for immune function, the researchers were curious not about which bacteria lived on the train compartment surfaces themselves, as had been examined in earlier studies in Boston and New York City subways, but about which were transferred to commuters’ hands.
The majority of microbes transferred were relatively harmless skin commensals, or bacteria normally living on the skin of other travelers. But, some pathogens were discovered as well.
In fact, according to Panagiotou, the best illustration of the mixing pattern came from antibiotic resistance genes. “In the morning, ARGs were only captured in a few lines but, by the evening, could be traced in all of them,” he said.
The aim was to better understand how urban planning can impact the types of bacteria we encounter so that studies investigating the microbial composition of train compartments can guide future public health strategies and public transit designs.
The good news for commuters is that higher traffic subway lines don’t carry higher health risks, in terms of either pathogens or antibiotic resistance genes.
The paper published in Cell Reports.
