Comparison of Aerobic and E. Coli Colony-Forming Units Isolated From Circulating Paper and Plastic $20 Canadian Banknotes
BC Institute of Technology: Environmental Health
Paper currency serves as an ideal breeding ground for microorganisms. Furthermore, the combination of its widespread use and its constant exchange make paper currency a likely agent for disease transmission. Recently the Bank of Canada has begun issuing plastic banknotes; theoretically, these plastic bills are less prone to contamination due to the inherent properties of plastic and specifically added antibacterial agents.
The purpose of this study was to determine if the new plastic banknotes harbor fewer bacterium than comparable (in age and denomination) paper bills. The objective was to sample both paper and plastic bills, and statistically verify whether there is (or is not) a difference in microbial load.
Standard microbiological methods were followed to test paper and plastic bills. The sample bills were tested using 3M aerobic colony Petrifilm plates and E. coli/coliform Petrifilm plates. The number of colonies counted on the Petrifilm plates (both types) was used to indicate associated contamination levels.
On average, the plastic bills had lower counts of aerobic bacteria and E. coli coliforms. However, there was not a statistically significant difference in contamination rates between plastic and paper bills (p-value: 0.090332). A low power (0.380125) indicates a beta error may have occurred and that a larger sample size is required to provide more accurate results.
The main conclusions resulting from this study include the following:
- Contamination rates for plastic bills are statistically similar to those of paper bills.
- On average (mean and median data), plastic bills had fewer aerobic bacteria and E. coli coliforms than paper bills.
- Canadian bills have a similar contamination rate as US bills. This study showed a 6.6% rate of heavily contaminated Canadian bills, compared to 7% in the United States (Lamichhane, Adhikary, Guatam, & Maharjan, 2009).
- Contamination rates varied greatly. While the majority of bills had relatively low contamination rates, a select few had extremely high rates.