MadSci Network: Microbiology

Re: Does Wasabi Kill Mouth Bacteria?

Date: Mon Jan 23 10:37:05 2006
Posted By: Stephanie Shaw, Post-doc/Fellow, UC Berkeley Environmental Science, Policy, and Management, UC Berkeley
Area of science: Microbiology
ID: 1137430097.Mi

Hello, and thank you for your question on whether or not wasabi can kill mouth bacteria. This is a very interesting topic. First let’s take a minute to discuss what types of bacteria live in this environment. Some of them are aerobic, which means they require exposure to oxygen to grow, and some are anaerobic, which means they do not require oxygen. Common types that live on your teeth are Streptococci species and Lactobacilli species. Please see the following Mad Scientist posts for more about these bacteria and how we control the numbers of these bacteria by brushing.


I have found information on the Internet (with a simple search tool like Google) regarding experiments done by the Japanese scientist Hideki Masuda on this topic. He published work that demonstrated certain chemicals called isothiocyanates in the wasabi inhibited the growth of Streptococcus mutans. If you have read the other MadSci posts, you know that these (and all cavity-causing) bacteria form a sticky layer called a plaque that is hard to remove from your teeth. This plaque is composed of the bacteria themselves, as well as chemicals you consume (sugar) and the bacteria produce (acids). Masuda discovered the chemicals in wasabi chemicals minimized the amount of bacterial cells that could adhere to the sugars on the tooth surface. I’m not sure if the wasabi actually killed the bacteria, or just kept it from growing on the tooth surface. This would be interesting to check yourself.

You mentioned that you have already done some experiments on this topic – that’s great! That’s how scientists get their start. You probably know that when we run experiments, we must try to make the entire process as similar as possible between all trials, except for the factor we are testing. Experiments must be based on an objective criteria (i.e. something that can be measured, like an amount, size, shape), and not an opinion (i.e. tastes “better”). Finally, the experiment needs to be repeatable – you should get the same results if you perform the test again, or if someone else does it.

Another very important thing that all scientists have to be very careful of before they can draw conclusions is to ensure they have also performed control experiments. This is a set of experiments identical to the one you want to test, except for the 1 factor that you test. If the outcome you hypothesized occurs in the experimental samples, but not in the control samples, that is good evidence that your factor causes the hypothesized results. If the outcome you expected also occurs in your control, then it is not due to the factor you originally thought.

In your case, you might want to try to grow some mouth bacteria on a solid medium like an agar plate. Then you can apply some wasabi to some of the samples. You can then visually measure how many, what type, and how large the bacteria colonies are that result over a week or two. You might want to test different types of bacteria (i.e. taken from different people), different types of growth medium (which can allow different bacteria to grow), and different amounts of wasabi. Be sure to talk to your science teacher about ways to avoid contaminating your samples, such as using sterile ways to make the growth medium and add the wasabi to it. You can use control samples to test for problems such as contamination. For example, you can mix enough medium to have some samples with bacteria but no wasabi, some with bacteria and no wasabi, and some with no bacteria and no wasabi. This will tell you if your medium is contaminated before you even start your experiment. Also, make sure you have lots of replicates of both your controls and your experimental samples. This will help you discover if the results you get are merely a matter of chance, or are likely to happen most of the time.

Talk to your science teacher at school or a doctor for safety reasons before you do these experiments. You wouldn’t want to grow bacteria that will make you sick, and you want to know how to dispose of your experiments when you are done with them. For example, you may need an adult’s help to soak your samples in bleach before throwing them away.

Good luck, and have fun!

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