Periodontitis and its possible contribution to preterm birth

Evidence is accumulating that gum disease can lead to chronic systemic inflammation throughout the entire body.  In fact, bacteria from the mouth may be entering the vasculature through the gums and can wind up in various places around the body, like in the plaques that cause heart attacks.  Another location that these mouth bacteria can end up is in the placenta of expecting mothers.  This is important because of the increasing association between the placental microbiome and preterm birth.  Researchers from Spain investigated this connection by determining the placental microbiomes of pregnant women with and without periodontitis.  The results of their study were published last week in the journal Oral Diseases.

The researchers measured the placental microbiomes of 57 pregnant women, as well as determined their periodontitis statuses.  They discovered that the abundance of placental bacteria was significantly higher in women with periodontitis.  In addition, they identified Fusobacterium nucleatum was significantly higher in the placentas of women with periodontitis.  Also, 90% of women who had either preterm birth or very low birth weight infants carried F. nucleatum, compared to 62% of full term pregnancies.

Interestingly, other studies have shown F. nucleatum in the mouths of folks with deep gum pockets, which strengthens this connection between the conditions.  It is strange to consider the relationship between the mouth and placenta, which have seemingly little in common.  However, the microbiome of both are connected by the vasculature, and they apparently share many of the same bugs.  Until further research can establish better connections between these pregnancy outcomes and the microbiome we recommend all expecting mothers to floss and brush their teeth every day.

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.

The oral microbiome of periodontitis patients has distinct profiles dependent on disease severity

A few weeks ago we discussed periodontitis, a bacterial infection of the gums that leads to inflammation and deep pockets to develop in which harmful bacteria can colonize. Periodontitis develops in association with dramatic changes in the makeup of the oral microbiome. Smokers and diabetics are more frequently victims of the disease. The study we discussed previously was one performed by researchers in Istanbul, Turkey in which they tested whether a probiotic lozenge could improve the patients’ condition. In a different, more recently published study concerning periodontitis, researchers in Connecticut and Massachusetts looked not to change the oral microbiome of patients suffering from periodontitis, but to organize and identify the microbial characteristics of the disease.

In the study published in Plos One, seventeen subjects, 8 of whom were diabetic, with Chronic Kidney Disease (CKD) and seventeen subjects without CKD, 3 of whom were diabetic, were studied.  All 34 subjects suffered from periodontitis. Samples were taken from each participant, from the deepest pockets in two different areas of the mouth. DNA was then isolated and sequenced to identify microbial communities in each individual. After much statistical analysis, the researchers found that the microbial communities tended toward two clusters, A and B, with type B communities correlating with more severe periodontitis. Group A subjects had communities with greater health-associated bacteria and cluster B communities were dominated by Porphyromonas gingivalis and Tannerella forsythia. Additionally, the analysis showed that diabetes and CKD are not correlated with a certain periodontitis microbial makeup.

A set-back of this experiment is the low sample size, which makes for less meaningful statistical analysis. Greater sample sizes of each cluster could give stronger claim to the findings of this study. However, this study does begin to clarify the bacterial community characterization of healthy, unhealthy, and severely unhealthy oral microbiomes. In addition, the results from this study could be used to ask further questions about the disease, including questions such as: what environmental factors cause the difference in clusters A and B? Do inflammatory diseases such as CKD and diabetes have anything to do with the severity of inflammatory response of periodontitis? Further analysis may allow us to answer these tough questions.

Probiotic lozenge fights periodontitis

Periodontitis is a complicated bacterial infection in the gums generally caused by a dysbiosis in the oral microbiome. It results is an immune response which inflames the gums, and after a long time causes pockets to develop in the gums that can be further infected by harmful bacteria. The usual treatment for this problem is the physical removal, or scraping away of the accumulated bacteria in these sensitive pockets. A team of researchers in Istanbul, Turkey did a study published by the Journal of Clinical Periodontology in which they tested the effects of a probiotic lozenge, Prodentis®, on the periodontitis condition.

Forty participants with periodontitis were involved in this double-blind study and randomly placed into a placebo group or a group that would consume a probiotic lozenge twice a day for three weeks, after brushing their teeth in the morning and at night. The probiotic used in this experiment was Lactobacillus reuteri, which is a bacterium we have discussed on the blog previously because of its probiotic characterization and because it commonly resides in the gut.

Samples were taken from the participants at day 21, 90, 180, and 360 to test for bleeding on probing (BoP), plaque (PI), gingival indices (GI), and probing depth (PD). The researchers found a significant reduction in probing depth on day 360 in the patients receiving the probiotic, compared to those receiving the placebo. Also, significantly fewer patients were at high risk for periodontitis disease at day 360 if they received the probiotic. As for the presence of L. reuteri in the mouth of participants taking the probiotic, on day 21 the bacteria was detected in six patients and on day 90 it was detected in eleven. No L. reuteri was detected in patients on days 180 and 360, making the levels not statistically different from the baseline sample before the start of the trial.

So what do the results of this study tell us? The participants receiving the Prodentis® probiotic lozenge had improved clinical and microbiological states compared to the placebo group. No long-term statement about L. reuteri colonization capabilities can be said however, because the microorganism was not detected in the probiotic group at days 180 and 360. At the very least, it seems the probiotic slowed the recolonization of harmful bacteria for up to six months before the levels returned to those pre-treatment, which is a promising step toward a more long-term treatment of periodontitis. 

Strange, parasitic microbiome bacteria may responsible for inflammatory diseases

Electron micrograph of a type of Actinomyces, the genus of the natural host of TM7, discussed in the paper.

There are many bugs in the microbiome that cannot be cultivated, and thus are incredibly difficult to study using normal culturing techniques.  We only know about these bugs through DNA sequencing, and it often difficult to draw any substantial conclusions from this information.  One such group of bugs that is highly abundant in the microbiome is the bacterial phylum TM7.  TM7 has been associated with numerous inflammatory diseases, like vaginosis, inflammatory bowel diseases and periodontitis, and DNA analysis shows that this bug has the ability to create many toxins.  Studying this bug could lead to breakthroughs in microbiome diseases, but until now it was unculturable.  Recently though, a team of scientists from around the United States were able to cultivate these bacteria and in doing so learned what makes this bacteria so unique, and possibly so pathogenic.  The results were published in PNAS.

The team aimed their investigation at the oral microbiome, because TM7 is abundant in the mouth and highly associated with periodontitis.  They took samples of spit and realized that TM7 only could grow when another bacteria, Actinomyces odontolyticus, was present.  When they cultured these bacteria together in a saliva-like media they realized that the TM7 was physically attached to the surface of A. odontolyticus.  Through further experimentation they learned that TM7 could never grow on its own, and needed A. odontolyticus to replicate.  Furthermore, TM7 is parasitic, and kills A. odontolyticus when they are starved.

The researchers then investigated the pathogenicity of TM7.  They learned that TM7 can evade detection by the immune system for itself and A. odontolyticus.  They also discovered that the particular strain of TM7 they were studying was antibiotic resistant.  Furthermore, sequencing of the TM7 showed the strain had amongst the smallest genomes ever discovered, and relies on the A. odontolyticus for production of many essential molecules, like amino acids.  However, TM7’s small genome is very dense in the production of virulent molecules and toxins, perhaps necessary for its parasitic nature, which could also affect its human host.

This study raises many interesting points about pathogens in the microbiome.  DNA sequencing is a great start to defining the microbiome, but often times culture, or in this case co-culture is necessary to drill down into the true virulence of bacteria.  For instance, prior to this study A. odontolyticus was considered to be associated with many inflammatory diseases, but these researchers showed that it is likely TM7, not A. odontolyticus that is the true culprit.  Alas, the complexity of the microbiome often times reveals many more questions than answers.

Mouth diseases and tooth loss may be caused by oral microbiome alterations

Chronic periodontitis is a prevalent inflammatory disease of the tissue around and supporting the teeth and is the leading cause of tooth loss in the United States. Scientists at the University of Florida recently published a study in Applied and Environmental Microbiology that studied the oral microbiome of 25 healthy individuals and 25 individuals with chronic periodontitis, in order to determine if there are any consistent microbial differences between the groups.

In the study, they found that patients with periodontal disease had an altered oral microbiome with microbial communitites that were more homogeneous than healthy individuals’.  They were able to identify two specific groups of bacteria, Fusobacterium and Porphyromonas, that were associated with periodontitis and another two groups of bacteria, Rothia and Streptococcus, that were prevalent in the majority of the healthy sites without periodontitis.  The scientists also identified several genes that were involved with various biological activities that were enriched in the oral microbiome of healthy individuals.

This study provides more insight into the possible microbial causes of chronic periodontitis, which is common among adults in the United States. While this study is limited because of its small sample size and its lack of diversity among severity of chronic periodontitis disease, it is still a great starting point for further inquiry into the disease. The scientists also compared their work to previous studies utilizing Human Microbiome Project (HMP) participants, though the HMP only included healthy individuals and excluded individuals with periodontal disease.  Further research could lead to the discovery of better ways to both treat and prevent the disease by altering the microbial communities of our mouth.