Sunday, September 16, 2007

It’s not rocket science, but…..

How many times do we hear that expression? And anyway, who decided that rocket science should be the datum for the rest of us? The success rate in that field could be improved a lot!

I want to show that simple experiments can be valuable.

Food poisoning doesn’t seem to be going away, in spite of the many articles published, television advertorials and the plethora of antibacterial cleaning agents on the market. The current concern about fresh poultry being a source of Campylobacter in the kitchen has lead to dishcloths being suggested as potential vectors of cross contamination. We all know this already, but we continue use them. Can we make them safer? Should we move to paper towels (not always convenient and perhaps environmentally unfriendly) or should we take the more expensive approach using cloths but discarding them more often? Should we boil them or put them in the dishwasher?

Standard fabric cloths were used in the kitchen for a week in the normal way. The cloths were then cut up and Standard Plate Counts were performed on Plate Count Agar. The samples were then treated by one of the following: economy wash cycle with a mdium load of dishes in a dishwasher; microwaving for 20 seconds on high (1 Kw); washing in hot water containing dishwashing detergent, or treating with hypochlorite solution containing 200ppm free chlorine. The samples were then counted again. Four complete replicates were performed. The results are shown below as a graph of log(APC/g) vs treatment; the error bars represent one standard deviation.

We can take several important points from these results:
• Used for a week, dishcloths become “microbial zoos” and a major source of contamination in the kitchen when the cloth is used to wipe benches etc.
• Hot water washing has little effect on the population size
• Bleach reduces the count by a factor of only10, probably because it is rapidly inactivated by the organic materials
• Dishwashing reduces the count by about 100x
• Microwaving is apparently the best treatment, reducing the count by a factor of over 1000x but there is still a very large population present, which can be spread around the kitchen.

This was a simple experiment that shows us some very important facts about the safety of everyday items in our food preparation areas. It might not be totally original, but that doesn’t affect the interpretation.

Who was the non-rocket scientist who made these measurements? The experiment was planned and conducted by Elisabeth Bakker, an eleven year old schoolgirl in Palmerston North, New Zealand, who submitted her research for a science fair project.

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