Dirty currency harbours pathogens, antibiotic-resistant genes

Microbes occupy almost every nook and cranny of the world – from volcano tops to clouds and even the currency notes in our wallets. A recent study on such notes at the Institute of Genomics and Integrative Biology, New Delhi, reports that they could be vectors of pathogenic microbes, some of which may even be transmitting antibiotic resistant genes¹.

Using microbiology culture techniques, scientists in India have previously surveyed fomites – inanimate objects such as clothing, currency notes or coins that transmit pathogens hand-to-hand. However, these results are often less pragmatic to be related to the natural milieu where the currencies are exchanged. For the first time, researchers led by Srinivasan Ramachandran have used metagenomics and high-throughput DNA sequencing technique to characterize the microbes.

“We have used this approach to characterize the microbial genetic material on paper currency notes of three frequently circulated denominations,” Ramachandran told Nature India.

The researchers isolated DNA from currency notes collected from random spots such as street vendors, grocery shops, snack bars, canteen, tea shops, hardware shops and chemists across New Delhi. They then sequenced the metagenome – the total DNA present on the currency notes – and computationally matched the obtained sequences with known ones. Earlier, scientists used to do this taxonomic identification by sequencing 16S-rRNA. But, “[Our] DNA sequencing approach offers advantages in providing additional information on the gene repertoire of organisms on the fomite,” Ramachandran said.

“It’s one of the first metagenomic studies coming from India,” said Jane Carlton, who led a similar study called the New York City Dirty Money Project, with PhD student Julia Maritz at New York University, USA.

Of the microbes identified, 70% were eukaryotes, 9% bacteria and less than 1% viruses. “We identified 78 pathogens including Staphylococcus aureus , Corynebacterium glutamicum , Enterococcus faecalis , and 75 cellulose degrading organisms including Acidothermus cellulolyticus , Cellulomonas flavigena and Ruminococcus albus ,” the researchers write. They also identified 78 antibiotic resistance genes, of which 18 were present in all the currency samples they collected.

While this study shows the potential of a fomite to carry antibiotic resistance genes, their method cannot find the origin of the genes or the pathogens. Also the mere presence of the resistance genes does not vouch for the pathogenecity that the currency notes might hide in them. “This is the starting point and without extensive follow-up studies, we would not be able to correlate [the presence of genes] with antibiotic resistance patterns in India,” Ramachandran added.

“There are potential disease-causing microbes that can be found on common…. this could be an additional tool to track public health trends,” said Carlton.

Deepak Kumar Raut, director of the Family Welfare Training and Research Center, Mumbai, says the study ‘scares’ by disclosing that Indian currency notes are an additional route of transmission of pathogens of communicable diseases. During epidemic outbreaks, contaminated currency notes could be a potential threat of infection spread. “If people follow simple principles of hand hygiene, contamination of currency notes can be avoided,” Raut told Nature India . But Ramachandran says it may be better to replace the aged notes with fresh ones.

Countries like Canada use polymer or plastic currencies, which not only have longer shelf-life but also limit pathogen transmission. Raut suggests introducing such cost-effective polymer bills in India to protect against contamination and counterfeiting. Ramachandran however feels that more studies are needed to prove their potential as a safe fomite.