Microbial Contamination and Survival Rate on Different Types of Banknotes

Abstract

In the COVID-19 pandemic context, numerous concerns have been raised regarding the hygienic status of certain objects we interact with on a daily basis, and especially cash money and their potential to harbor and transmit pathogenic bacteria. Therefore, in the present study, we analyzed different currency bills represented by British pounds (5 £, 10 £ and 20 £), Romanian lei (1 leu, 5 lei and 10 lei), U.S. dollars (1 $, 5 $ and 10 $) and Euros (5 €, 10 € and 20 €) in order to evaluate the bacterial survival rate and bacterial adherence. We used five reference microorganisms by American Type Culture Collection (ATCC, Manassas, VA, USA): Staphylococcus aureus ATCC 6538, Escherichia coli ATCC 8739, Enterococcus sp. ATCC 19952, Salmonella enterica subsp. enterica serovar Typhi ATCC 6539, and Listeria monocytogenes ATCC 7644. Microorganisms were selected in accordance with the criteria of prevalence, pathogenicity, opportunism, and incidence. However, Maldi-TOF analysis from samples taken from the banknotes revealed only a few of the common pathogens that are traditionally thought to be found on banknotes. Some of the most important factors for the survival of pathogenic agents on surfaces are the presence of organic matter, temperature and humidity. Our data showed that Salmonella enterica survived 72 h on every banknote tested, while L. monocytogenes tended to improve persistence in humid conditions. Survival rate is also influenced by the substrate composition, being lower for polymer-based banknotes especially for Salmonella enterica, Listeria monocytogenes and Enterococcus sp. The adherence of bacterial strains was lower for polymer-based banknotes British pounds and Romanian Leu, in contrast to the cotton-based U.S dollars and Euro banknotes. The risk of bacterial contamination from the banknote bills is high as indicated by both a strong survival capacity and low adherence of tested bacteria with differences between the two types of materials used for the tested banknotes.

Keywords: bacterial adherence; banknotes; currency; fomite; pathogens; public health.

Figure 1

Bacterial survival recorded as CFU/cm² at 22 °C, 35% humidity, on various banknotes at five time points (0 h, 12 h, 24 h, 48 h and 72 h) (* p-value = 0.03).

Figure 2

Bacterial survival recorded as CFU/cm2 at 37 °C, 65% humidity, on various banknotes at five time points (0 h, 12 h, 24 h, 48 h and 72 h) (* p-value = 0.02).

Figure 3

Influence of temperature of incubation on survival of different bacterial strains.

Figure 4

Bacterial survival rate on different banknotes—Comparison of 12 h after inoculation to 72 h post inoculation.

Figure 5

Logarithmic reduction trend line for bacterial survival at 12 h compared to 72 h; SA-Staphylococcus aureus, EC— Escherichia coli, EN— Enterococcus sp., SE— Salmonella enterica, LM— Listeria monocytogenes; (p < 0.05).

Figure 6

Bacterial recovery rates • = positive control (initial inoculum of 10⁵ CFU/mL in saline buffer) (p < 0.05).

Figure 7

Adherence pattern of Staphylococcus aureus, E. coli, Enterococcus sp., Salmonella enterica and Listeria monocytogenes strains on different types of banknotes.