Sunday, July 12, 2015

The Hidden Microbial World On Your Cash And What It Means For Your Health

We all know cash can be super dirty! <SOURCE>
We have all thought and talked about how dirty money is. Those notes are transferred all over the world, touched by thousands of people, and find themselves in every sort of hygienic situation. But how dirty is money really? What kinds of microbes (bacteria, viruses, etc) are sitting on your cash, and can they make you sick? To provide us with some insight into these questions, Jalali S et al recently reported a study in which they used high throughput sequencing techniques to look at the money microbiome and its potential for causing disease. The goal of this post is going to be briefly discussing the main points of the paper, and what they mean for us in general. This work was published in the open access journal PLOS ONE, so you can go ahead and check it out for yourself for free.

As far as methods go, the research group relied on pretty standard shotgun metagenomic sequencing approaches. As a brief refresher from a previous post discussing these methods, this means the microbial genomes (including bacterial, fungal, etc) were sequenced. This allowed the researchers to see what kinds of bacteria were present on the bills, and what kinds of genes these microbes contained (allowing predictions about functionality). To get the DNA from the cash, the group collected pools of three Indian currency values (10, 20, 100), suspended the notes in DNA extraction buffer for 10-12 hours, and extracted/sequenced the DNA.

A figure from the paper, showing the distribution of
microbes found on money. (Figure 2A)
So what were the highlights of the group's findings? They started by looking at what organismal DNA was present on the differently valued bills. They primarily found eukaryotes, including Rhodophyta (Red Algae) and Viridiplantae (Green Algae). Bacterial and archaeal DNA was also present on the notes, although in much less abundance (see figure to the right). This is interesting because the microbes seem to be largely environmental plant and algal matter, and not so much bacterial. Of the bacteria they found, they did find potential pathogens (remember these are only DNA signatures of potential pathogens) in addition to bacteria known to degrade cellulose, which might affect the lifespan of the note.

Moving on from asking "what microbes are present?" to "what are they doing?", the group looked at the functional potential of the microbes found on the notes. They did do a general survey of all of the genes present, but this is pretty abstract and difficult for us to sink our teeth into. As a nice specific investigation, the group looked at the antibiotic resistance genes present on the notes. Their sequencing approach, as well as PCR validation to those genes, revealed 78 potential antibiotic resistance genes. While this is interesting and further highlights a source of antibiotic gene resistance transfer in our environment and culture, it is so important to take this with a grain of salt because these are only potential antibiotic resistance genes.

In the end, what can we say about this paper? There are two main points you should leave with. First is that the microbial communities of money are primarily environmental eukaryotes including algae, with a much smaller fraction being bacteria. In retrospect, this makes sense because our money is constantly in contact with the environment, so it seems to pick up the environmental DNA. The second point is that money harbors potential antibiotic resistance genes, which suggests it could play a role in transmitting antibiotic resistance. While this does not mean your cash will give you a terrible, antibiotic resistant infection (or at least it is highly unlikely), it does highlight currency as another means of pathogenic gene transfer.

You still don't need a lab safety suit to handle
your cash. <SOURCE>
This paper has some interesting points, but also raises other cool questions. How do the microbial communities differ between types of currency like the Euro or USD? How does a specific bill's microbiome change over time? How does the microbiome of your hand change after touching money, and what gets left behind? These all seem like great questions to answer, and perhaps those are on the horizon for this research group. We are going to have to stay tuned.

So what does all of this mean for your life? Honestly not a whole lot. Out of our own experiences, we intuitively know money can be dirty, and this paper further supports that by telling us more about how dirty it is. But next time you pay for something, think about the bacteria, eukaryotes, and other microbes that bill left behind on your hands and in your wallet. This is pretty cool stuff.

Works Cited

Jalali S, Kohli S, Latka C, Bhatia S, Vellarikal SK, Sivasubbu S, Scaria V, & Ramachandran S (2015). Screening currency notes for microbial pathogens and antibiotic resistance genes using a shotgun metagenomic approach. PloS one, 10 (6) PMID: 26035208

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