New Delhi: Currency notes, one of the most commonly exchanged objects, are known to harbour disease-causing microbes. Now, a group of Indian scientists has found antibiotic resistant-genes along with bacteria and viruses in rupee notes, giving the phrase dirty money a potential health twist.

This team of scientists, from the Institute of Genomics and Integrative Biology under the Council of Scientific and Industrial Research, studied rupee notes using—possibly for the first time—a shotgun metagenome sequencing approach. This method employs a relatively new analytics and sequencing approach with complex data to identify microbes in a sample.

The scientists found 78 pathogens and 18 antibiotic resistant-genes in the samples they tested.

The results of their analysis, reported in the June issue of the scientific journal Plos One, showed that out of the discovered microbes, 70% were eukaryota (which include fungi and protozoa), 9% were bacteria, and less than 1% were archae (single-celled organism lacking nucleus in the cells) and viruses.

Pathogens and other micro-organisms can thrive in paper notes because of the rough surface which allows them to settle for long periods. The level of contamination depends on how long the note has been in circulation, its capacity to absorb moisture, and its texture.

Recently, several attempts have been made to investigate the microbial population in currency notes in various parts of the world.

A study published last year in Biomedicine and Biotechnology, an open access peer-reviewed journal, pointed to high levels of pathogenic or potentially pathogenic bacteria contamination in banknotes around the world—96.25% in Palestinian notes, 91.1% in Colombia, 90% in South Africa, 88% in Saudi one Riyal paper notes and 69% in Mexico’s polymer notes.

To be sure, the Indian scientists point out that the presence of genetic material does not necessarily mean the presence of live organisms. “This is especially true in the case of pathogens, where the mere presence of the genetic material from the pathogen would not necessarily mean the sample is infective, though the presence of genetic material would necessarily mean the sample was contaminated at some point in time," the June study said.

One drawback highlighted in the Plos One study was that the methodology used to analyse the microorganisms in the notes cannot identify the organisms harbouring the antibiotic resistance genes. “Our approach provides a holistic view of the diversity of pathogens associated with currency notes. The present study provides an interesting pipeline for a variety of future applications, including bio-surveillance of exchangeable fomites for infectious agents," said the authors.

The methodology could, however, be used to identify sources for drug resistant-genes, and to analyse the sterility and cleanliness of critical areas such as operation theatres and medical equipment, and as an approach to track and identify sources of epidemics. The authors said the method could also be used to screen for potentially emerging infectious agents, including agents of bioterrorism.

Another study, published in Journal of Research in Biology in 2014, found that rupee notes used by public institutions such as banks, hospitals and municipal corporations in India were highly contaminated with pathogenic bacteria, followed by rupee notes used by butchers and food sellers.

Andreas Voss, author of a paper on money and transmission of bacteria and the factors that influence transmission of microorganism from banknotes, said more research was needed to find out whether the bacteria and virus found in rupee notes were being transmitted.

“Obviously banknotes and coins get contaminated as anything else, thus I believe what is really missing is a link, showing transmission. So far this is interesting, but the proof of the pudding would be in transmission, which does need further investigation," said Voss, professor of clinical microbiology and infection control hospital epidemiology at the Radboud University Nijmegen in the Netherlands.

There have been unfounded scares regarding currency notes and the spread of disease. During the 2003 SARS outbreak, some Chinese banks sterilized soiled notes with ultraviolet rays. In 2014, during the Ebola outbreak in East Africa, media reports that currency notes could spread the virus were not confirmed by scientists.