Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Biological Sciences

First Advisor

Dr. Jim O' Mahony


Staphylococci are a diverse group of bacteria that cause diseases ranging from minor skin infections to life-threatening bacteremia. Methicillin-resistant S. aureus (MRSA) is the most common multidrug-resistant nosocomial pathogen in Europe estimated to cause 170,000 infections resulting in more than 5,000 deaths and additional healthcare costs of approximately €380 million annually (Kock et al., 201 1). Whilst rarely life-threatening, coagulase-negative staphylococci (CoNS), in particular S. epidermidis are responsible for the majority of indwelling medical device failures, causing intrinsically resistant biofilm infections, estimated to cost $2 billion per year in additional healthcare costs in the U.S. alone (Otto, 2009).

It is well accepted that circulating currency has the potential to harbour disease- causing pathogens and, staphylococci are among the most frequently isolated from international currencies. However, studies investigating prevalence and persistence of such pathogens on euro currency are virtually non-existent or scarcely reported.

The objectives of our study therefore, were to assess the prevalence of staphylococci present on a sample of circulating €10 banknotes in the Cork city area and subsequently evaluate the level of antibiotic resistance among such. A further objective was to undertake the first study on the persistence of S. aureus on euro currency and in doing so assess the efficacy of incorporating bioluminescence into persistence studies. And finally having carried out the afore mentioned, ascertain whether circulating euro currency demonstrates a potential risk to the public.

In this study, we report 97% of €10 banknotes screened (n=155) harbour multiple species of staphylococci. In total, 150 staphylococci isolates were recovered and of these, 71 were S. aureus and 79 were CoNS. An inversely proportional relationship between banknote condition and numbers of staphylococci isolates was observed throughout the study. Additionally, there was no observed seasonal variation (winter/spring months).

Subsequently we found that 62% of the staphylococci demonstrated resistance to at least one of the ! "'* line antibiotics (52.11% of S. aureus isolates and 76.71% of the CoNS isolates). The most common resistance observed among S. aureus was against erythromycin, and for CoNS isolates, the greatest resistance was recorded against both erythromycin and mupirocin. Multi-drug resistance was seen in 31.18% of the resistant isolates, specifically, 8 S. aureus isolates and 21 CoNS isolates. Multi-drug resistance profile type I was most frequently observed among S. aureus isolates and profile type I and II were most commonly observed among the CoNS isolates. In terms of an overall trend. Multi-drug resistant (MDR) among CoNS was much greater than among S. aureus. These findings are consistent with previous studies, given that the most frequently isolated member of CoNS, {S. epidermidis) has been widely implicated in multi-drug resistance dissemination. In subsequent analysis, S. aureus was shown to persist on euro banknotes and coins for significant periods (on average, 16.67 days on €2 coins and, 19.33 days on €10 banknotes) using indirect bioluminescence as a marker.

In conclusion, our study demonstrated the ability of euro currency to act as a reservoir for the dissemination of potentially pathogenic microorganisms and, has revealed the relatively high levels of antibiotic resistance and multi-drug resistance among contaminating staphylococci species in circulation. For the first time, we demonstrated the ability of S. aureus to persist on euro currency for a significant period. We report, that euro currency and in particular, banknotes have the potential to pose a serious health risk especially among the immunocompromised in society. Therefore, we recommend the introduction of intervention measures such as polymer-based banknotes, and the introduction of cashless transactions within high risk healthcare environments in attempts to curb the widespread dissemination of resistant pathogens.

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