Where does bacteria REALLY lurk on the subway?

June 29, 2016  23:48

It is no surprise that subway trains are colonized by bacteria.

Lurking on ticket booths, platforms, seats and hand grips are trillions of different germs that transfer from commuters to surfaces where they fester ready to transfer back to other unsuspecting travelers.

But, while bugs on the subway are inevitable, a new study suggests there are steps people can take to avoid the grimiest spots on the underground.

A team of researchers from Harvard T.H. Chan School of Public Health, took to the Boston subway, known as the T, armed with swabs.

Their aim, to discover where bacteria hides and which strains are rampant.

The researchers found the highest number of microbes were found on hanging grips, followed by seats or touchscreens. 

And they were surprised to discover, while trillions of microbes inhabit the subway, the majority are not harmful to humans.

Their investigations found hanging grips, seats and touchscreen ticket booths were the areas a traveler is most likely to pick up germs.

Senior author of the study, Dr Curtis Huttenhower, associate professor of computational biology and bioinformatics, said: 'We were surprised to find that the microbes that we collected on surfaces that people touch - and sometimes sneeze on - had low numbers  of worrisome pathogens or antibiotic resistant genes. 

'These environments have drastically lower virulence profiles, in fact, than are observed in a typical human gut.

'They're exactly what you'd run into shaking somebody's hand. 

'We were surprised by how normal a lot of the samples looked. Even when we looked closely, there was nothing unusual or dangerous about the microbes we found.

'It shows that, in the absence of something like flu season, all of the germs you run into, even in a crowded environment like the T, are normal. 

'Our findings establish a baseline against which deviations can be used as an early warning system to monitor public health.'

Dr Huttenhower's team suggest monitoring the bacteria present on the subway could provide an early warning system for the emergence of public health threats, such as a flu outbreak or a rise in antibiotic resistance.

With the support of the Massachusetts Bay Transit Authority, the researchers collected 100 samples by swabbing seats, seat backs, walls, vertical and horizontal poles, and hanging grips inside train cars on three subway lines.

In addition, they tested touchscreens, and walls of indoor and outdoor ticketing machines at five subway stations. 

Detailed data were collected on the environment in which each sample was taken, before the samples were then studied using metagenomic sequencing.    

The scientists discovered that the type of surface - and how humans interact with it - was the greatest determinant of microbial community structure.

Skin, and microbes associated with the mouth, transferred by touching and coughing or sneezing, were found on surfaces such as poles and hand grips.

Meanwhile, vaginal microbes, which can be transferred through clothing, were found on seats.  

All surfaces were dominated by normal human skin microbes, with the bacterial families Firmicutes, Proteobacteria, and Actinobacteria each responsible for over 20% of the microbial community. 

The team found low levels of gut and oral microbes such as Lachnospiraceae, or those from the Veillonella and Prevotella families.

'I didn't expect the grips to have that much DNA on them, because they're relatively small and seem to be used less often,' said lead study author Tiffany Hsu, a graduate student at the school. 'But porous surfaces can collect microbes more efficiently than something solid like a metal pole.' 

Greater numbers of non-human microbes, such as those seen in plants, were found on outdoor ticketing touchscreens.

Furthermore, the researchers noted little variation was seen between the different geographical locations and trains, which served different demographics.

In addition, the team found very few microbes capable of causing disease or associated antibiotic resistance.

Dr Huttenhower said: 'This indicates that the real pathogenic potential detected in the Boston subway is very low.' 

The findings, published online today in the American Society for Microbiology's journal mSystems, are consistent with previous microbial DNA-sequencing based studies that have revealed that bacteria communities in the built environment are greatly influenced by their human occupants.

The researchers note that further study is needed to explore the separate influences of human contact, surface type, and surface material to help identify mechanisms through which bacteria form and persist on various surfaces. 

Ms Hsu added: 'Our next steps are to find out which microbes are dead or alive and which can be transferred between people.'

This study was supported by a grant from the Alfred P. Sloan Foundation. 

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