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.

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

The placental microbiome

Microbiome populations have been well-characterized in many distinct body-sites.  Interestingly, there is a lack of knowledge in the microbiome of the placenta, an environment that was long thought to be sterile.  Investigating the placenta is important toward understanding the microbiome in human development, especially in light of previous evidence demonstrating that human microbiota populations fluctuate extensively in the first year(s) of life.  The placenta is the cradle of life for fetal development, leading researchers from Baylor School of Medicine to study the microbiome of this tissue.  Placenta samples were collected and analyzed to characterize the placenta microbiome, and explore links to fetal development and microbiome compositions. 

320 placenta specimens were collected, and PCR was used to characterize bacterial populations.  The Meta genome sequencing revealed that the placenta microbiome harbored unique abundances in specific bacteria compared to other body sites.  E. coli in particular had the highest species abundance.  Interestingly, the microbiota populations were most similar to the oral microbiome.  Species such as Prevotella tannerae and Neisseria, known to populate the mouth, were also abundantly present in the placenta.  Further analysis confirmed that the placenta bacteria were indeed most similar to bacteria specifically found in the tongue, tonsils, and gingival plaques. 

The researchers also demonstrated an association between placental microbiome composition and healthy births or births with complications.  Specifically, a significant association was shown between distinct placental microbiome populations and pre-term birth.  Taxa such as Durkholderia were shown to be enriched in the placentas of those who delivered their infants preterm, whereas Paenibacillus was abundant in normal terms placental specimens. 

This study reveals a couple very interesting associations between cross-site microbiome similarities and disruptions in compositions that appeared to be linked to preterm birth.  Although not definitive evidence, these findings could lead to some important research in the future.  There were a few confounding elements to this study, such as other body site samples occurred in non-pregnant subjects, or the fact that the mass of the placental microbiota was particularly low.  However, these findings certainly raise awareness of the uniqueness of the placental microbiome, and what this means in terms of the microbiome entering the developing fetus.  It will be interesting to see what further research can reveal about this relationship. 

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The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

The vaginal microbiome changes during and after pregnancy

The vaginal microbiome is critically important to a healthy pregnancy, and studies have shown that vaginal dysbiosis during pregnancy can lead to infection and preterm birth.  In order to help understand what the microbiome looks like throughout and just after pregnancy, researchers from England performed longitudinal studies on 42 pregnant women.  They published their results last week in Nature Scientific Reports.

The scientists sequenced the microbiomes of the 42 women throughout their pregnancies, and then for the 6 weeks afterwards for some of the women.  They discovered, in agreement with other literature on the subject, that the vaginal microbiome becomes dominated by Lactobacilli species during pregnancy.  The Lactobacilli are thought to prevent pathogens from colonizing the vagina because they produce lactic acid which decreases the overall pH of the vagina, and they secrete antibacterial toxins.  These Lactobacilli are also important as they are normally the first to colonize the new infants' guts after they pass through the birth canal. 

The researchers also learned that the microbiome shifts away from Lactobacilli and towards a more diverse microbiome in the period immediately following birth.  The new bacteria that colonize are often associated with vaginosis, and these can lead to inflammation and infection of the birth canal in some women.  The scientists suspect this shift occurs because there is a sudden drop in estrogen production upon removal of the placenta.  The increase in circulating estrogen is thought to be important for Lactobacilli colonization, so it makes sense that the rapid decrease in estrogen decreases Lactobacilli abundance.

Finally, this study showed that there were geographic and ethnic variations to the pregnant microbiome.  While each microbiome was associated with a healthy pregnancy, there were important differences, especially on the species level.  For example, Asian and Caucasian women’s pregnant microbiomes were dominated by Lactobacillus gasseri, while this species was absent in black women’s pregnant microbiomes.

This paper helps show the normal progression of the microbiome during and after pregnancy.  With the mounting evidence that the microbiome is often a contributing factor to preterm birth and some post-partum diseases, papers like this one are important to some day discovering the mechanistic basis for our microbiome's association with these issues. 

Please email for any comments, news, or ideas for new blog posts.

The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.