“You can either embrace the dirt and the germs as part of the risky joy of living in an exciting, overpopulated metropolis, or you can spend lots of mental real estate obsessing over whether you touched a few extra microbes when you got on the subway.” – Zack Love
When I first moved to Boston from “car country” and spent over two hours a day on the subway (called the T) to get to and from lab, I feared I would get sick all the time from touching things or sitting next to someone coughing up a lung. But was my fear of the T warranted?
Microbiome of the Boston MBTA and other subway systems
A paper from Curtis Huttenhower’s lab published in mSystems last week addresses the fears we may have of public transportation. These researchers sampled different surfaces on the subway trains and stations in Boston and identified what bacteria are present using 16S rRNA gene sequencing and shot-gun metagenomic sequencing.
The microbes found on the subway system surfaces were mostly human skin and oral commensals (the microbes that live on our skin or in our mouth without causing us harm). Three other studies have also analyzed the microbial compositions in subways systems. Microbiologists in Hong Kong and in New York City sequenced the microbial communities in the air of their subway systems and another study in New York City profiled the microbial communities in the subways and public parks. These studies also found that the samples contained mostly skin commensals and some soil microbes.
Microbiomes affected by surface materials and other environmental parameters
The Huttenhower lab also found that both human body interaction and surface material influence the microbial communities found on the surfaces. For example, though the backs and the bottoms of the subway seats were made of the same material, the microbes from the seat bottoms were enriched in vaginal commensals (possibly transferred through clothing) when compared to the seat backs. Vinyl seats also had a different microbial composition than polyester seats. Touchscreens located in outdoor stations had a different species composition than touchscreens located in indoor stations indicating that environmental parameters also play a role.
The team also determined that there were few genes associated with antibiotic resistance or virulence in their samples (these genes are dramatically more represented in our guts). Therefore, there is little pathogenic potential from the subways and it is actually pretty difficult to transfer pathogens from one person to another through a surface. In studying the microbes present in built environments, it is possible to establish a baseline microbial profile to which deviations from this may be considered potential public health threats.
Do these results change your perception of “bad germs” in public places?
i remember reading the reports when it first came out and it did beg the question, in my mind, about the role of commensals in general.
I haven’t been keeping up, but what role do these commensals serve in harboring antibiotic resistance and what is their capability in transferring them to more virulent species?
Also I’m pretty certain a few commensals that were listed are more the “commensals assuming a person is healthy.”
Great comments. There is likely not much genetic transfer going on in bacteria from these surfaces. In a previous post about microbes in office spaces, the authors of the paper discussed how the microbial communities on urban surfaces were likely dormant and inactive as the microbial compositions never changed with time. The microbes would require water and nutrients to become metabolically active again.
In other environments where the microbes are actually metabolically active, transfer of antibiotic resistance genes and virulence genes can occur. Examples of this would include the human gut, animal gut, soil, marine and freshwater systems, etc. In these environments, it is possible for commensal bacteria to acquire virulence or antibiotic resistance genes and pass them along to pathogens and can become a public health concern.