By Jamie Hulzebos
Do you ever pick-up food from the ground after dropping it and then eat it? Some people do it daily, others are disgusted by this practice. People that do pick up their food and thereafter eat it often justify their behaviour by referring to the five-second rule. This “rule” is known to most of us, and implies that bacteria “wait” five seconds before contaminating dropped food. It has even been subject to scientific research. High school student Jillian Clarke won an Ig Nobel Prize, a parody of the Nobel Prize, for her research internship at the University of Illinois on this topic [1]. So, what can be concluded from this and other research on the five-second rule?
Jillian Clarke found that placing gummy bears and cookies for five seconds on ceramic tiles contaminated with Escherichia coli will result in contamination of the food [2]. She swabbed the floors around the University, including the lab, hall dormitory and cafeteria, to see how many bacteria she could find on those floors. She repeatedly found no culturable bacteria. This does not mean that there are no bacteria present, as some bacteria will not transfer easily to a cotton swab. More experienced researchers from Clemson University, South Carolina, focused on the differences between floor coverings and transfer of bacteria. They found that Salmonella Typhimurium, a well-known pathogenic bacterium sometimes found on raw meat or poultry, can survive for up to 4 weeks on dry surfaces and almost immediately transfers to food [3]. Surprisingly, carpet had the lowest transfer rates compared to tile and wood. At last, researchers from the State University of New Jersey found that longer contact time with the ground resulted in more bacteria transfer, but other factors like the nature of the food and surface were more important [4]. These researchers from South Carolina and New Jersey did not conduct any field research like Jillian Clarke, but would you take the chance of eating your dropped food, if you knew that these bacteria can survive for that long?
Unsurprisingly, the researchers from New Jersey concluded that the five-second rule is a giant oversimplification of bacteria transfer, even though it has an origin in factual data. There are many more important factors, such as the nature of the food, e.g. wet or dry, and floorcovering. Clarke found that University floors are cleaner than we might think, but shouldn’t we be wary drawing conclusions from a high school student’s research? Moreover, none of these researchers incorporated fungi or viruses in their studies, while these microorganisms can also be pathogenic.
Now, will you eat that dropped food?
- Winners of the Ig Nobel Prize. Available at: https://www.improbable.com/ig/ig-pastwinners.html#ig2004. Retrieved on October 19, 2017.
- ACES College News. If You Drop It, Should You Eat It? Scientists Weigh In on the 5-Second Rule. September 2, 2003. Available at: http://news.aces.illinois.edu/news/if-you-drop-it-should-you-eat-it-scientists-weigh-5-second-rule. Retrieved on October 19, 2017.
- Dawson, P. et al. Residence time and food contact time effects on transfer of Salmonella Typhimurium from tile, wood and carpet: testing the five-second rule. Journal of Applied Microbiology 102, 945-953 (2007).
- Miranda, R.C., Schaffner, D.W. Longer contact times increase cross-contamination of Enterobacter aerogens from surfaces to food. Applied and Environmental Microbiology 82 (21), 6490-6496 (2016).
