Dirty money: E.coli and MRSA super bugs on our banknotes

A very interesting study on dangerous bacteria that can survive on our money won an Ig Nobel prize

Image Credit: Alexander MIls via Unsplash - HDR tune by  Universal-Sci

Image Credit: Alexander MIls via Unsplash - HDR tune by Universal-Sci

Recently the 2019 Ig Nobel prizes have been awarded at Harvard University. The idea behind the Ig Nobel awards is to celebrate unusual scientific achievements by making people laugh at first and then make them think about the subject at hand.

One of the award-winning studies that caught our eye this year focused on dirty money, literally. Dutch, German, and Turkish scientists worked together to find out which banknotes provide the best environment for dangerous bacteria to survive and potentially play a key role in bacterial transmissions from people to people.

The researchers studied paper money from different countries, including US dollar and Euro banknotes. First they inoculated some dangerous microorganisms: Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli (E.coli / ESBL) and Vancomycin-resistant Enterococcus (VRE) into unused banknotes (These are types of bacteria that can cause problems in health care). Following that injection the researchers checked after 3, 6 and 24 hours if any of the dangerous bacteria were still alive. 

The cleanest

The Croatian Kuna and Indian Rupee bills turned out to be the cleanest. At the first direct swab, the Croatian Kuna did not yield any of the three dangerous pathogens while the Indian Rupee only produced VRE. After 3 hours, scientists only found single colonies, and after six hours, the VRE bacteria had disappeared entirely. 

The dirtiest

It turns out that from all the bills that were tested the Romanian Leu scored the worst. This is probably due to a polymer fiber, used in the banknotes to prevent the creation of fake money, that appears to sustain bacteria for a long time. The Leu banknotes yielded all three multi-drug resistant pathogens that were tested (namely MSRA, VRE, and ESBL producing E.coli) at the first direct swab. In addition, all three types of bacteria still remained on the bills in large numbers after three hours and six hours. The Romanian Leu was also the only currency that still produced dangerous microorganisms (VRE) after 24 hours of drying.

Image Credit:  moerschy via Pixabay  - HDR tune by  Universal-Sci

Image Credit: moerschy via Pixabay - HDR tune by Universal-Sci

Euro and Dollar banknotes

The European and American currencies performed somewhere in between the previously mentioned currencies. At the first direct swab, US dollar bills yielded large amounts of MRSA, multiple segments of VR, and a tiny amount of ESBL. Euro banknotes generated a small amount of VRE and a large amount of ESBL but no MRSA at their first swab.

After six hours, the MSRA had disappeared from the US dollar bills, and only small amounts of VRE and ESBL remained. Meanwhile, Euro bills only contained a small quantity of ESBL after that amount of time. Luckily all bacteria had disappeared on both currencies after 24 hours of drying. 

Should we be worried?

Andreas Voss, one of the authors of the study, stated in an NPO interview that it is important for central banks to pay attention to dangerous bacteria when designing banknotes. However, people shouldn't be too worried as our immune systems should be able to handle a tiny amount of these bacteria. 

Nonetheless, it is important to keep hygiene in mind. Simple things like washing your hands before touching your mouth, eyes, nose, and/or wounds should go a long way in preventing contamination. 


Sources and further reading: Money and transmission of bacteriaIg Nobel PrizeNPO interview with Andreas Voss


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