Bacteria in the mouth

Monday 22 October 2012 5:52PM (view full episode)

Our mouths are filled with bacteria that are responsible for the decaying of teeth and periodontal disease. Researchers at the University of California Los Angeles have investigated this problem.

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Norman Swan: One of the places these so-called old friends once lived is in our mouths. These days, our mouths are filled with bacteria that make our teeth decay—dental caries—and inflame our gums—periodontal disease. Research in California is trying to make all that a thing of the past.

Professor Wenyuan Shi is Chair of Oral Biology at the School of Dentistry at the University of California, Los Angeles.

Wenyuan Shi: Over the last 120 years we've been using very much the surgical approach, trying to control the infections. So when you see a dentist he always removes plaque and all that. But the problem is sometimes—joking—it is a Stone Age technology. When you use mechanical removal trying to combat a bacterial infection it's very difficult.

Norman Swan: Essentially that's the whole business—decay, you get these bugs very early in life, your first few months of life, and they live with you for the rest of the time causing tooth decay, unless you're very lucky.

Wenyuan Shi: Very true. So the bacteria in our oral cavity is actually causing two of the major diseases, tooth decay and periodontal disease. And in the US alone it burns $100 billion a year.

Norman Swan: And so if you could get rid of these bugs permanently or at least in the long term, you'd be preventing these infections.

Wenyuan Shi: Yes. It could be everybody's dream to get rid of those bacteria. But it's very difficult because the mouth is paradise for the bacteria. It's got the water, the food, the right temperature, and we're constantly inoculating the bacteria through food and kissing. So it's very difficult to get rid of them. There's a lot of products on the market trying to get rid of them, like mouthwash, like Listerine. But the problem with all those products is they're a broad spectrum killer, and the bacteria grow very fast, so by the time you finish your mouthwash it only takes a few hours for them to come back.

Norman Swan: And it kills off everything.

Wenyuan Shi: Yes, you will kill good and bad bacteria at the same time. So if I step back for a second, there is more than 1,000 species and over 100 trillion bacteria in everybody's mouth.

Norman Swan: Puts you off kissing...

Wenyuan Shi: Yes, you're getting a lot of new kinds through kissing, so you always need to be careful who you are kissing.

Norman Swan: So there are trillions of bacteria in your mouth. Some of them you need, and some of them you don't.

Wenyuan Shi: Yes. Only a few of them are bad, which are called dirty dozen. One of them is strep mutans, which is the main bacteria causing the tooth decay. Now the problem is when this bacteria is hiding in the jungle of the rest of the bacteria. When you use a broad spectrum killer you do kill the bad strep mutans but you destroy the jungle as well. And the consequence of that is always helping the strep mutans to come back first.

Norman Swan: So what have you done?

Wenyuan Shi: If you have the weeds growing in the grass and if you use a general herbicide you actually kill your weeds while you kill your grass, and it's always the weeds come back first. So we decided to develop a weed-specific killer, ultimately preventing the weeds coming back.

Norman Swan: Because the grass chokes out the weeds after they've gone.

Wenyuan Shi: That's right. So to achieve that what we did is we built something we called smart bomb.

Norman Swan: Smart bomb?

Wenyuan Shi: It is a smart bomb literally. We took a broad spectrum killer, in this case it's an anti-microbial peptide.

Norman Swan: A small protein, if you like, that's targeted against the bug.

Wenyuan Shi: That's right. We took a non-smart drug and put in a homing device in front of it. And it would rely on the homing device targeted to deliver the killer.

Norman Swan: You were telling me before we started that strep mutans excretes a pheromone.

Wenyuan Shi: That's right. So bacteria are a lot more smarter than we imagine. And for them to live in the environment with a thousand species, they actually use various languages to communicate with themselves including pheromones. And there's a wonderful study we did, where we literally put the sex pheromone behind the killer, which I called fatal attraction. So in this particular drug, which is called C16G2, hasn't got a good name yet…

Norman Swan: Smart bomb sounds pretty good.

Wenyuan Shi: [Laughs] So the C16 was actually a pheromone used for strep mutans, used for communication purposes, especially when they're under stress, and they actually use it for communicating with each other, counting how many of the same species in the jungle. So we rely on that, you know, put the killer behind that. So while they're thinking this is a communication signal, they get more than they bargained for.

Norman Swan: And it literally blows up the bacteria.

Wenyuan Shi: That's right.

Norman Swan: As you say, bacteria are very smart. Have they found a way to work round this?

Wenyuan Shi: You know, being a microbiologist for 30 years, I'm never surprised by what they will do. They manage to develop resistance to everything, so sooner or later they will develop resistance to this particular approach as well. But compared with all those other antibiotics, we minimise the chance for them to do that.

Norman Swan: Tell me about the pilot study you did.

Wenyuan Shi: It was really surprising, because right now the best drug to prevent tooth decay gives you about 12 hours protection. In this particular study, which lasted for four days, and we only gave one treatment, it actually gave total protection for four days.

Norman Swan: And how did you apply it?

Wenyuan Shi: It was delivered as a mouth rinse.

Norman Swan: So literally rinsing your mouth for a minute or two did it.

Wenyuan Shi: That's right. It was actually 40 seconds. And we only targeted the bad bacteria and let the good bacteria take over. That's why it provides the long term protection.

Norman Swan: There are bugs that inhabit other parts of our body we might not need—particularly our bowels. Could this be applied elsewhere, do you think?

Wenyuan Shi: Yes, totally. One of the greatest advancements in microbiology in the last 20 years is to realise we're only 10% human. Actually 90% of the cells living in the human body are bacteria, from the skin, to the nose, to the oral cavity, to the gut flora. And our ultimate health is not only the health of our human cells but also the bacteria which live with us. And the smart bomb technology is really providing the way, and you can modulate it without disrupting the flora.

Norman Swan: So how would you get it to the bowel?

Wenyuan Shi: You can coat them with different ways and you can deliver them any places you want.

Norman Swan: Professor Wenyuan Shi is Chair of Oral Biology at the School of Dentistry at the University of California Los Angeles.


Sullivan R et al. Clinical Efficacy of a Specifically Targeted Antimicrobial Peptide Mouth Rinse: Targeted Elimination of Streptococcus mutans and Prevention of Demineralization. Caries Research 2011;45:415-428


Professor Wenyuan Shi
Chair of Oral Biology
School of Dentistry
University of California Los Angeles


Dr Norman Swan
Brigitte Seega

Comments (3)

Add your comment

  • notsobright :

    24 Oct 2012 10:47:26am

    Thanks for the story, but there's not much enlightenment to be got from for the rest of us. What does this smart-bomb contain? When, if would it be available for the masses? How much will it cost? Is it a simple herb that you can grow in your veggie garden? Please tell us also about this more useful stuff.

  • D. Chamberlain :

    25 Oct 2012 3:46:30pm

    Is this "pheromone communication" to do with triggers for biofilm formation?

  • Bereft :

    02 Nov 2012 8:49:53am

    Dear Norman Swan,

    What should the average punter do with this story?! It's disappointing because such press-release type material does nothing towards alleviating the dental misery in this country for those on low incomes. They can listen to the radio, access the internet, but not a dentist, let alone see a periodontist. I think as the national broadcaster you can be part of the solution with a program that would also have practical application.

    What has definitely helped the condition for me was not Colgate sponsored, but using colloidal silver, garlic gloves, hot salt water, and a good ionic toothbrush. It was all hear-say and trial and error when some more scientific input such as from the Health Report wouldn't have gone astray. But none of the search words of these remedies revealed much of interest regarding dental health.

    Your Average Punter