"Disgust is intuitive microbiology"
(Steven Pinker)
We are often nauseated by reports about the bacteria found on household items. Sponges, dishwashers and coffee machines are sprawling with bacteria! News reports
on these findings usually feature a scary headline and then go on to
report that most of the found bacteria are benign, only a select few
could potentially be harmful under certain conditions. But the damage is
done: Bacteria are perceived as disgusting and their mere presence
symbolizes the necessity to clean. But does our intuitive microbiology match the actual microbiology?
Let's have a look at the numbers to see how good our intuitive microbiology is:
The sponge-study found up to 5.4 * 10^10 bacteria per cubic centimeter of sponge material! Yes, 54 billion! In a cube with only 1cm edge length. That is roughly 1 bacterium for every US dollar that Mark Zuckerberg owned in 2017! But is it really that much? The number of bacteria in the environment can be hard to comprehend, because it is so big. Afterall, we are made up of the equal numbers of human and microbial cells!
So, let's compare the 54 billion bacteria per cubic centimeter sponge material to another study that looked at bacteria in the environment: on a single grain of sand in the North Sea, you can find up to 100,000 bacterial cells! And that equals a bacterial density of up to 2.3 * 10^10 bacteria per cubic centimeter of sand! Yes, 23 billion bacteria, approximately 1 bacterium for every US dollar of net worth of Phil Knight (founder of Nike) in 2017! [Check the end of the post for my calculation] And not just one strain of bacteria but 1000s of species on a single grain.Granted, the sponge still holds more than twice as many bacteria as the sand, but the numbers are in the same ballpark.
People avoid the beach for many reasons (seagulls, rip tides, and even sharks)
but few people think of bacteria when it comes to hazards at the beach.
Rightly so, because a high number of bacteria does not equal a threat by them: Microbes are important members of ecosystems!
We as humans would probably not be around anymore if we encountered more harmful than harmless (or even helpful) bacteria in our environment. Instead, we have a very stable truce with most microbes of our environment. Often pathogenic bacteria don't have the chance to grow to dangerous numbers, because their habitated is already very rich in other bacteria. In the case of kitchen sponges, the intuition to use a new one frequently seems to be a good approach (better than trying to sanitize it) because the sponge gets in close proximity with our food, but generally we should give microbes more love - they truly deserve it!
Let's have a look at the numbers to see how good our intuitive microbiology is:
The sponge-study found up to 5.4 * 10^10 bacteria per cubic centimeter of sponge material! Yes, 54 billion! In a cube with only 1cm edge length. That is roughly 1 bacterium for every US dollar that Mark Zuckerberg owned in 2017! But is it really that much? The number of bacteria in the environment can be hard to comprehend, because it is so big. Afterall, we are made up of the equal numbers of human and microbial cells!
So, let's compare the 54 billion bacteria per cubic centimeter sponge material to another study that looked at bacteria in the environment: on a single grain of sand in the North Sea, you can find up to 100,000 bacterial cells! And that equals a bacterial density of up to 2.3 * 10^10 bacteria per cubic centimeter of sand! Yes, 23 billion bacteria, approximately 1 bacterium for every US dollar of net worth of Phil Knight (founder of Nike) in 2017! [Check the end of the post for my calculation] And not just one strain of bacteria but 1000s of species on a single grain.Granted, the sponge still holds more than twice as many bacteria as the sand, but the numbers are in the same ballpark.
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We as humans would probably not be around anymore if we encountered more harmful than harmless (or even helpful) bacteria in our environment. Instead, we have a very stable truce with most microbes of our environment. Often pathogenic bacteria don't have the chance to grow to dangerous numbers, because their habitated is already very rich in other bacteria. In the case of kitchen sponges, the intuition to use a new one frequently seems to be a good approach (better than trying to sanitize it) because the sponge gets in close proximity with our food, but generally we should give microbes more love - they truly deserve it!
Stay tuned for another post on the bacteria in your coffee machine and what they have to do with sewage-treatment plants!
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Note: 2.3 * 10^10 bacteria is only an approximation! I assumed grains of sands were spherical, which they are usually not.
The number approximates the maximum concentration: 100,000 bacteria was the maximum found by the authors. Also, grains were between 202 µm and 635 µm in diameter, I used the smallest grains (radius = 101 µm) for my calculation, hence the concentration is higher:
Volume of a grain of sand:
Bacterial concentration is calculated by dividing the bacteria per grain by the volume of each grain:
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Note: 2.3 * 10^10 bacteria is only an approximation! I assumed grains of sands were spherical, which they are usually not.
The number approximates the maximum concentration: 100,000 bacteria was the maximum found by the authors. Also, grains were between 202 µm and 635 µm in diameter, I used the smallest grains (radius = 101 µm) for my calculation, hence the concentration is higher:
Bacterial concentration is calculated by dividing the bacteria per grain by the volume of each grain:
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