How public transport spreads microbes


train

It’s common knowledge that public transport’s a great place to pick up a cold… and new research has quantified it

The Hong Kong researchers also identified one subway line that could be a potential source of antibiotic resistance, they said.

Published in Cell Reports, the study sampled the hands of volunteers using eight lines on the Hong Kong subway system, morning and night, for three weeks – including one line that crossed into the Chinese mainland – to map the bacteria people pick up on their skin.

Most of the microbes they found were harmless, but the study identified one line that may serve as a potential source of antibiotic resistance.

The genes giving the antibiotic resistance started out on one line in the morning and spread to become common on every line in the later hours of the day.

“In the morning, each line has unique microbial features reflecting the regions it passes, but with more and more people using the subway during the day, the microbial communities of all the lines become more similar, dominated by human skin commensal bacteria,” says Gianni Panagiotou, a systems biologist at the Hans Knoell Institute in Germany and the University of Hong Kong.

“The Metro is constantly cleaning every surface that we touch, but the train compartments have little personal space–passengers are squashed there, and we are talking about one of the busiest and densest cities in the world.”

The hundred-mile-long Hong Kong subway system serves nearly five million people.

In partnership with architect Chris Webster, Mr Panagiotou and his team wanted to examine 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.

They then aimed to see if the microbiome itself would inherit the tidal effects of the traffic flow enough to vary over traveling time.

“With five million people riding the subway every day, the fingerprint of the whole city had to be there,” says Mr Panagiotou.

To simulate the average commuter experience, the researchers sent volunteers through the subways for half an hour during both the morning and evening rush hours, sampling the skin on their hands after each.

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 travellers, the researchers said.

However M Panagiotou said that 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 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.

“Instead, we want to better understand how urban planning can impact the types of bacteria we encounter so that studies like ours investigating the microbial composition of train compartments may guide future public health strategies and public transit designs.”

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