For some time now, various forces have been pushing us away from using paper money to pay for things. That goal may have a hidden bonus: Cash, it turns out, is crawling with bacteria.
Although researchers have known for some time that microbes can, and do, live on money, a new study from Hong Kong shows that these bacterial communities are more substantial than previously suspected. Cash, it turns out, could be an excellent way to monitor the microbes circulating through a city.
To examine the extent to which bacteria live on money, researchers from the University of Hong Kong collected 15 paper bills from cashiers at 12 hospitals and three metro stations (the underground transportation system) across that city. Their first step was to check whether microbes could survive on the bills. To do this, they scraped bacteria from the cash and placed them in various cell cultures—petri dishes containing different types of agar, a substance derived from algae that serves as a growth medium. The results, published in Frontiers in Microbiology, showed that the bacteria grew readily, indicating that they were living on the money.
The most common bacterial strain on the Hong Kong bills was Propionibacterium acnes, which is linked to skin acne. One type of P. acnes found on currency was first isolated from a patient with sarcoidosis, an inflammatory disease, in 2013. Among the 15 sample bills, about 36 percent of the bacteria were pathogenic, meaning capable of infecting humans. The infections caused by those bacteria are not necessarily dangerous. But the finding emphasizes the fact that money is most definitely a vehicle for potentially contagious microbes.
Also common among the samples was a bacterium called…