Bacterial contamination and their tolerance in banknotes and coins surrounding the area of Chiang Mai University Hospital in Chiang Mai Province

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Ponrut Phunpae
Chanjuti Sriruan
Ratchadaporn Udpoun
Santhana Buamongkol
Sudjai Pawichai
Autchar Ruangpayuk
Watchawan Chairuangwut


Background: Currency including banknotes and coins are used in everyday life by everyone. It is, therefore, a universal medium for carrying potentially pathogenic bacteria which can spread and cause infection in the population. Thus, it is of interest to study the bacterial contamination in currency used daily in Chiang Mai province, of which there is scant information.

Objectives: To study the quantity and types of bacterial contamination on banknotes and coins circulating in the area surrounding Chiang Mai University Hospital in Chiang Mai province and examine the tolerance of detected bacteria on the currency.

Materials and methods: Banknotes and coins, totaling 343 samples, were collected from circulation in the area surrounding Chiang Mai University Hospital in Chiang Mai. The bacterial contamination was studied based on culture methods and identified by morphological and biochemical tests. To examine the bacterial tolerance, the contaminated bacteria recovered from the currency, including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii, were tested. These bacteria were inoculated on banknotes and coins and the viability of the bacteria at various time points was examined.

Results: The amount of bacterial contamination on banknotes, which are linen fibers, was higher than those on coins, which are opaque metals. The gram-positive bacteria were found in a higher amount than gram-negative bacteria, in both banknotes and coins. Human skin flora and pathogenic bacteria, especially S. aureus and pathogenic Enterobacteriaceae, were detected. The bacterial tolerance study revealed that S. aureus, the gram-positive cocci, showed a decrease of viability on banknotes and coins within 6 hours. Meanwhile, gram-negative bacilli presented a decrease of viability in 6 and 1 hours on banknotes and coins, respectively. The bacterial tolerance testing by used and unused currency showed the same results.

Conclusion: All banknotes and coins circulating in the area surrounding Chiang Mai University Hospital in Chiang Mai province were demonstrated to be contaminated with bacteria, some of which might be pathogens and dangerous to users. Gram-positive bacteria has higher tolerance than gram-negative bacteria on currency. Bacterial tolerance on banknotes is longer than on coins. The knowledge obtained is advantageous for people in general as an awareness of these harmful bacteria when using the currency.


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Phunpae, P., Sriruan, C., Udpoun, R., Buamongkol, S., Pawichai, S., Ruangpayuk, A., & Chairuangwut, W. (2018). Bacterial contamination and their tolerance in banknotes and coins surrounding the area of Chiang Mai University Hospital in Chiang Mai Province. Journal of Associated Medical Sciences, 51(3), 171-179. Retrieved from
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