Scientists at Clemson University conducted an interesting study on the so-called “5 Second Rule” – You know, the one that claim it’s ok to eat food dropped on the floor if its only been soaking up germs for 5 seconds or fewer?
It is obvious that food dropped onto a bacteria covered floor would collect some bacteria. But how much? Does it collect more as the seconds tick by? Enough to make you sick?
Prof. Paul L. Dawson and his colleagues at Clemson have now put some numbers on floor-to-food contamination.
Their bacterium of choice was salmonella; the test surfaces were tile, wood flooring and nylon carpet; and the test foods were slices of bread and bologna.
First the researchers measured how long bacteria could survive on the surfaces. They applied salmonella broth in doses of several million bacteria per square centimeter, a number typical of badly contaminated food.
I thought that most bacteria were sensitive to drying out, but after 24 hours of exposure to the air, thousands of bacteria per square centimeter had survived on the tile and wood, and tens of thousands on the carpet. Hundreds of salmonella were still alive after 28 days.
Professor Dawson and colleagues then placed test food slices onto salmonella-painted surfaces for varying lengths of time, and counted how many live bacteria were transferred to the food.
On surfaces that had been contaminated eight hours earlier, slices of bologna and bread left for five seconds took up from 150 to 8,000 bacteria. Left for a full minute, slices collected about 10 times more than that from the tile and carpet, though a lower number from the wood.
What do these numbers tell us about the 5-second rule? Quick retrieval does mean fewer bacteria, but it’s no guarantee of safety. Even if a floor or a countertop, or wrapper carried only a thousandth the number of bacteria applied by the researchers, the piece of food would be likely to pick up several bacteria.
The infectious dose, the smallest number of bacteria that can actually cause illness, is as few as 10 for some salmonellas, fewer than 100 for the deadly strain of E. coli.
Of course we can never know for sure how many harmful microbes there are on any surface. But we know enough now to formulate a new version of the 5-second rule: If you drop a piece of food, pick it up quickly, take five seconds to recall that just a few bacteria can make you sick, then take a few more seconds to think about where you dropped it and whether or not it’s worth eating.
It is obvious that food dropped onto a bacteria covered floor would collect some bacteria. But how much? Does it collect more as the seconds tick by? Enough to make you sick?
Prof. Paul L. Dawson and his colleagues at Clemson have now put some numbers on floor-to-food contamination.
Their bacterium of choice was salmonella; the test surfaces were tile, wood flooring and nylon carpet; and the test foods were slices of bread and bologna.
First the researchers measured how long bacteria could survive on the surfaces. They applied salmonella broth in doses of several million bacteria per square centimeter, a number typical of badly contaminated food.
I thought that most bacteria were sensitive to drying out, but after 24 hours of exposure to the air, thousands of bacteria per square centimeter had survived on the tile and wood, and tens of thousands on the carpet. Hundreds of salmonella were still alive after 28 days.
Professor Dawson and colleagues then placed test food slices onto salmonella-painted surfaces for varying lengths of time, and counted how many live bacteria were transferred to the food.
On surfaces that had been contaminated eight hours earlier, slices of bologna and bread left for five seconds took up from 150 to 8,000 bacteria. Left for a full minute, slices collected about 10 times more than that from the tile and carpet, though a lower number from the wood.
What do these numbers tell us about the 5-second rule? Quick retrieval does mean fewer bacteria, but it’s no guarantee of safety. Even if a floor or a countertop, or wrapper carried only a thousandth the number of bacteria applied by the researchers, the piece of food would be likely to pick up several bacteria.
The infectious dose, the smallest number of bacteria that can actually cause illness, is as few as 10 for some salmonellas, fewer than 100 for the deadly strain of E. coli.
Of course we can never know for sure how many harmful microbes there are on any surface. But we know enough now to formulate a new version of the 5-second rule: If you drop a piece of food, pick it up quickly, take five seconds to recall that just a few bacteria can make you sick, then take a few more seconds to think about where you dropped it and whether or not it’s worth eating.
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