Dirty Money
PAPER BILLS CARRY ACNE-CAUSING BACTERIA AND OTHER PATHOGENS
VARIOUS FORCES have been pushing us away from paper money, including mobile phone apps. That goal may have a hidden bonus: Cash, it turns out, is crawling with bacteria. Although scientists have known for some time that microbes can, and do, live on money, a new study shows that these bacterial communities are more substantial than previously suspected.
To examine the extent to which bacteria live on money, researchers from the University of Hong Kong collected 15 paper bills from 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.
The most common bacterial strain was Propionibacterium acnes, which is linked to skin acne. One type of P. acnes found on currency was first isolated in 2013 from a patient with sarcoidosis, an inflammatory disease. Among the 15 sample bills, about 36 percent of the bacteria were pathogenic, meaning they are capable of infecting humans. The infections caused by those bacteria are not necessarily dangerous, but the finding shows that money is definitely a vehicle for potentially contagious microbes.
Also common among the samples was a bacterium called Acinetobacter. All known Acinetobacter species can cause human infections, but most such infections are caused by one called Acinetobacter baumannii, which can cause pneumonia or wound infections in people with weak immune systems, chronic lung disease or diabetes.
This new study joins a growing stack of research seeking to keep track of bacterial communities in cities. Scientists are trying to find the most reliable places to look for potentially dangerous pathogens emerging across the world. Wastewater, doorknobs and other surfaces and substances with which we have frequent contact may all serve as such “alert systems,” says Andreas Voss, a microbiologist who teaches infection control at Radboud University Medical Center in the Netherlands. Voss thinks wastewater is probably the most accurate source for microbe monitoring, especially if it can be traced to its origin point, be that a farm, a home or a public toilet.
Voss notes that the ability of bacteria to grow on money depends on several factors, including what the money is made of, the geography of the region (coastal environments and humid climates may be more conducive than drier, inland places) and sanitation.
Can money make you sick? Voss considers the chances of acquiring a disease from contact with paper bills to be negligible, but the study’s authors write that their findings “unveiled the capabilities of this common medium of exchange to accommodate various bacteria, and transmit pathogens and antibiotic resistance.” In other words, while paper bills do not currently pose a widespread health threat, they could allow us to follow the microbes among us and spot a new threat if one does emerge.