Abstract
In this study we report the underlying reasons to why bacteria are present on banknotes and coins. Despite the use of credit cards, mobile phone apps, near-field-communication systems, and cryptocurrencies such as bitcoins which are replacing the use of hard currencies, cash exchanges still make up a significant means of exchange for a wide range of purchases. The literature is awash with data that highlights that both coins and banknotes are frequently identified as fomites for a wide range of microorganisms. However, most of these publications fail to provide any insight into the extent to which bacteria adhere and persist on money. We treated the various currencies used in this study as microcosms, and the bacterial loading from human hands as the corresponding microbiome. We show that the substrate from which banknotes are produced have a significant influence on both the survival and adherence of bacteria to banknotes. Smooth, polymer surfaces provide a poor means of adherence and survival, while coarser and more fibrous surfaces provide strong bacterial adherence and an environment to survive on. Coins were found to be strongly inhibitory to bacteria with a relatively rapid decline in survival on almost all coin surfaces tested. The inhibitory influence of coins was demonstrated through the use of antimicrobial disks made from coins. Despite the toxic effects of coins on many bacteria, bacteria do have the ability to adapt to the presence of coins in their environment which goes some way to explain the persistent presence of low levels of bacteria on coins in circulation.
Highlights
Money is the most recognisable exchange matter with a secure value that is used by people to obtain goods and services, or to accumulate as a safe gathering of wealth
Notwithstanding a hastily moving society where credit cards, mobile phone apps, near-field-communication systems, and cryptocurrencies such as bitcoins are rapidly replacing the use of hard currencies [1,2], cash exchanges still make up a significant means of exchange for small value purchases, while cash is still commonly used in developing countries for high value purchases
Rather than focusing on the occurrence of potentially pathogenic microorganisms on currency per se, we focused on currency as a microcosm
Summary
Money is the most recognisable exchange matter with a secure value that is used by people to obtain goods and services, or to accumulate as a safe gathering of wealth. A search of available literature uncovered in excess of 100 publications that report on the presence of microorganisms on banknotes and/or coins since the late 1800s, with roughly two thirds of those papers being published in the last decade This considerable interest in the hygienic status of currency predominantly focuses on the isolation of bacteria, and sometimes fungi. Rather than focusing on the occurrence of potentially pathogenic microorganisms on currency per se, we focused on currency (both banknotes and coins) as a microcosm (an environment that support a heterogeneous population of microorganisms that are defined by their typical usage). Microcosms represent simplified physical ecosystems used to simulate and predict the behaviour of natural environments, but under controlled conditions Both banknotes and coins are predominantly handled by multiple humans through touch. We argue that the most likely source of the microorganisms on currency originates from humans [13,14,15,16,17,18] and could be considered as a heterogeneous microbiome
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