Myth of dirty money exposed
Wednesday, 12 July 2006
The long-held belief that you can catch disease from handling money may be exaggerated, says an Australian researcher.
A study by Dr Frank Vriesekoop, a lecturer in food science at the University of Ballarat, has found there are generally few pathogenic bacteria on banknotes and coins.
"The potential [to spread disease] is still there. But I don't think it's all as bad as it's made out," he says.
He will present the results of his study at the Australian Institute of Food Science and Technology annual conference in Adelaide today.
He will also tell delegates that his team found low levels of antibiotic-resistant bacteria on banknotes and coins.
Vriesekoop worked with New Zealand researchers from the Eastern Institute of Technology to look at the types and number of bacterial cells found on money on both sides of the Tasman.
The researchers analysed coins and banknotes from mainly small food outlets such as cafes, small supermarkets and shops like butchers and bakers, all places where the person who handles food is also likely to handle money.
Back in the laboratory, the researchers bombarded the coins with pulses of sound to dislodge any microbes on the surface. They then identified and counted the number of viable bacteria.
The researchers found few bacteria, typically 1 or 2 cells per square centimetre.
"Some batches appeared to be sterile," says Vriesekoop.
He suspects that the copper and nickel in the 20c pieces and the aluminium and bronze in the dollar coins are toxic to many bacteria.
The banknotes needed a different approach. They were placed in a device like a
mini-washing machine that beats and swirls the notes in a special liquid. The
scientists then analysed the liquid for microbes.
This time, the counts were higher, typically 10 cells per square centimetre and
varied much more between samples.
The researchers found a range of organisms on coins and notes, including those that cause food poisoning or diarrhoea.
These included low levels of coliforms such as Escherichia coli, bacteria typically associated with the colon and generally linked with poor hygiene; Staphylococcus aureus, a common organism with some strains that can cause disease in susceptible people; and Bacillus cereus, which causes food poisoning if cooking does not kill its tough spores.
But what surprised the researchers was evidence of salmonella bacteria.
"It did worry me a bit," says Vriesekoop.
Also surprising was the number of bacteria that were resistant to one or more commonly prescribed antibiotics, like amoxycillin, roxithromycin and cefaclor.
"This was higher than I anticipated," he says.
Potential to cause disease?
While Vriesekoop says levels of bacteria were generally low, we still don't know how easily they are transferred from money to humans.
"Do they grow or die? We don't know," says Vriesekoop, adding that this might be the subject of future research.
He also hopes to work with the Royal Australian Mint to see how the raised surfaces of coins affect bacterial survival.
Vriesekoop is also co-ordinating an international comparison of bacterial levels on currency from the US, UK and Ireland.
The results, which he hopes to have at the end of the year, will help to confirm whether Australia's polymer notes are less hospitable to bacteria than paper notes used in most of the world.