Table 2.
Inhibitory influence of coin disks (12 × 1 mm) on the growth of a range of bacteria as represented by zones of inhibition in average and standard deviation, and mm radius (n = 12).
| Coinage * | Zone of Inhibition (mm) | ||||||
|---|---|---|---|---|---|---|---|
| Currency | → Bacteria → → |
S. aureus | S. Typhimurium | E. coli | L. monocytogenes | C. sakazakii | |
| ↓ Make-up ↓ | |||||||
| USA 1c | Copper plated zinc | 37.1 (3.7) | 30.9 (6.9) | 34.3 (7.1) | 37.3 (9.0) | 45.5 (3.8) | |
| UK £1 | 70% copper, 24.5% zinc, 5.5% nickel | 13.8 (1.7) | 3.9 (0.9) | 1.3 (0.8) | 2.8 (1.1) | 8.9 (1.1) | |
| AU $1; NZ $1 | 92% copper, 6% aluminium, 2% nickel | 4.9 (0.4) | 3.8 (1.1) | 2.5 (0.7) | 2.1 (0.7) | 7.6 (1.6) | |
| MEX 10c | 100% stainless steel | 12.2 (2.9) | 2.5 (0.6) | 1.7 (0.6) | 2.0 (0.7) | 0.0 | |
| NZ 50c | Nickel plated steel | 2.6 (0.5) | 4.2 (0.8) | 4.6 (0.9) | 3.9 (1.2) | 5.6 (0.56 | |
| UK 10p; USA 5c; AU 20c | 75% copper, 25% nickel | 8.8 (2.3) | 2.3 (0.6) | 2.3 (1.1) | 1.5 (1.1) | 18.4 (1.4) | |
| UK 20p | 84% copper, 16% nickel | 7.9 (2.1) | 2.2 (1.0) | 2.0 (0.6) | 1.8 (0.9) | 16.4 (1.7) | |
| USA 10c; 25c | 92% copper, 8% nickel | 6.6 (1.4) | 1.8 (0.3) | 2.3 (1.1) | 1.9 (0.4) | 13.1 (1.6) | |
* In order to standardise the methodology across a number of different metallic currency coins we rolled all coins down to a 1 mm thickness and punched them out to create disks with a diameter of 12 mm.