Identifying probiotics using healthy individuals for preventing oral disease

The oral microbiome consists of many hundreds of species of bacteria, some harmful and some beneficial. The importance of a healthy microbiome should be stressed not only because having clean, white teeth looks good but because diseases like periodontitis increase risk of other issues such as respiratory infections and inflammatory diseases. Having unhealthy teeth can cause more systematic problems than you would think. Probiotics, different from antibiotics, are one way that microbiome science is combating the colonization of harmful bacteria in the body. Many researchers have investigated using probiotics to maintain a normal healthy oral microbiome, and in a new study published last week, scientists researched probiotics that may reduce the smell of “bad breath” that is caused by volatile sulfur compounds, and prevent cavities and periodontitis.

The study, performed by researchers at the Yakult Central Institute for Microbiological Research in Tokyo, Japan (a division of Yakult, the makers of yogurts and probiotics),  was aimed toward finding new potential probiotic candidates. Thirty-two volunteers were recruited and selected based on factors such as non-smoking habits, no large cavities or bleeding on probing, and no bad breath. Oral bacteria samples were taken from multiple specific locations in the mouth of the volunteers. The bacteria were cultured in a lab and tested for the characteristics that follow: lack of production of volatile sulfur compounds (causes bad breath) and water insoluble glucan (causes cavities), antibacterial activity against bacteria that cause periodontitis, ability to healthily adhere to teeth and cells in the mouth, and caused no infections in an artificial mouth system or in a rat model.

After culturing in a lab and testing the criteria on 896 oral samples from the 32 participants, the study found that Lactobacillus crispatus YIT 12319, L. fermentum  YIT 12320, L. gasseri YIT 12321, and Streptococcus mitis YIT 12322 are good candidates for probiotics.  The next step is to now test for these probiotics’ effects in the mouths of many people, and likely develop a product.  Interestingly, L. crispatus and L. gasseri are two of the major bacterial strains found in a healthy vaginal microbiome, and perhaps this suggests a route of access for these bacteria to access the vagina. In any case, the promise of new ways to help maintain a healthy oral microbiome is exciting, and it is encouraging to read papers from major companies that have the ability to actually manufacture products in this space.

Walk, chew gum, and fight cavities all at the same time

Chewing gum has been suggested to have many cognitive benefits such as increasing focus and alertness, improving memory, and controlling, besides its obvious benefit of making breath smell minty fresh.  What about gum's effect on our microbiome though?  Could gum help prevent cavities in the same way as tooth brushing or flossing?  In order to find out, researchers from the Netherlands and Wrigley, the gum company, recently published the results of a study in PLoS One that set out to answer the question: how much oral bacteria is trapped and removed by chewing gum?

In order to test the hypothesis, volunteers chewed gum for various times for up to 10 minutes. The researchers then used different quantitative and qualitative analyses, such as culturing and genomic analysis, to measure the amounts of bacteria collected in the gum.  The researchers found that the chewing gum does indeed trap around 100 million bacteria, which is about the same as brushing your teeth with a new, clean toothbrush without using toothpaste. They also state that chewing gum could prevent biofilm formation, much like tooth brushing.  Finally, they concluded that the longer gum is chewed, the fewer bacteria it removes from the mouth.

This study in quantifying bacterial removal by gum was preparing the researchers for their next project, which is to intelligently design gum to prevent cavities.  As we know there are healthy and harmful bacteria in the oral cavity, but the study did not investigate which types of bacteria were removed.  If gum could be designed that preferentially adsorbs and removes acid-forming bacteria like Streptococcus mutans then it could be highly effective in eliminating cavities.  We look forward to reading more about this project, and in the meantime, if you’re going to chew gum, try and make sure it’s sugar free.

Could ice cream prevent cavities?

We know that the oral microbiome hosts a wide variety of bacteria, some good, and some that cause cavities.  Those that cause cavities do so by producing acid as they break down the food in our mouths.  Researchers in India are trying to discover if probiotics could help alter the oral microbiome so there is a decrease in the bacteria that commonly cause cavities.  In their study they investigated a type of ice cream sold in India that has the probiotics Bifidobacterium bifidum and Lactobacillus acidophilus mixed in with the ice cream.  The researchers were interested in the effects the probiotic ice cream on the levels of bacteria and fungi in saliva, namely Streptococcus mutans, Lactobacillus acidophilus, and Candida albicans, because these three bacteria are the main causes of tooth decay.  The results were recently published in the Journal of Dental and Medical Sciences.

In the study, the researchers gave 20 participants one dish of ice cream each day for 10 days that either contained the probiotics or did not.  The researchers examined the bacteria in the participants’ saliva both before and after the ice cream intervention.  The results showed that consumption of probiotic ice cream caused a significant reduction of both S. mutans and C. albicans, and an increase in the number of L. acidophilus when compared to controls.  The increase in L. acidophilus is not surprising because the ice cream contained L. acidophilus. The researchers highlighted that in other studies of people eating Lactobacillus acidophilus, it did not persist in the individuals’ mouths.  Overall, two of the cavity causing bacteria decreased in abundance and one, which was in the probiotic ice cream, increased in abundance.

We must admit that the rigor of this study was highly lacking, so we don’t want anyone to take these results too seriously. While more research needs to be done to determine if probiotic ice cream can actually help prevent cavities and tooth decay, any study that recommends eating it is fine by me.  It’s obviously important to brush your teeth every day, but it’s definitely more fun to eat ice cream than to floss!

Saliva regulates our oral microbiome

We know that saliva is important during eating and digestion, but researchers from Harvard and MIT investigated how saliva may be influencing the microbiome.  In an article recently published in Applied and Environmental Microbiology the scientists describe results that show saliva also includes molecules that influence oral bacteria so as to prevent cavities.

Cavities are formed when bacterial biofilms form on teeth and produce acids that go on to dissolve tooth enamel.  Saliva, which flows through the mouth, works to wash away these bacteria and helps remineralize teeth.  Beyond this, it contains molecules called mucins, which are a component of body mucous that are known to influence the microbiome and which have been associated with many autoimmune disaeases.    Before now, it was unknown how salivary mucins impacted the oral microbiome.

Researchers combined the bacteria Streptococcus mutans, which is known to be one of the many bacterial culprits behind cavities, with salivary mucins in the presence of artificial teeth.  They discovered that while the mucins did not prevent the bacteria from growing and proliferating, they did in fact prevent the S. mutans from attaching to the artificial teeth.  In fact over 95% of biofilm formation (which can cause cavities) was decreased between control samples and samples with the mucins.  The scientists noted that in the samples with mucins the cells simply never formed biofilms, and stayed in the planktonic (i.e. free floating) form.  They speculate that the mucins either physically prevent binding or are somehow changing the genetics of S. mutans so as to prevent production of binding proteins.

Follow-up studies in human subjects that compare the presence of mucins with cavity abundance would be interesting to see.  We all know people who, despite brushing and flossing multiple times a day, still seem to get cavities (myself included!), and others who, despite not going to a dentist in years and never brushing, don’t get any cavities at all.  Perhaps the concentration of mucins is responsible, and perhaps we could add mucins to toothpaste and forget about cavities all together.