Scientists knew there was an amoeba loitering in our gums. What they didn’t know was whether to be worried about it.
Entamoeba gingivalis likes to hang out in the angry little nooks called gingival pockets. On teeth left unbrushed and unflossed, oral bacteria adhere and secrete chemicals that inflame nearby gums. The resulting swollen, red, readily bleeding tissues creep down the teeth, forming bacteria-filled pockets where tooth meets gum. This is called gingivitis.
In Western nations, where oral hygiene and dental care are presumably the best in the world, a staggering half of adults over 30 suffer from this malady. When gingivitis goes south, becoming periodontitis, Entamoeba tends to move in.
Scientists also knew that E. gingivalis is closely related to the gut pathogen Entamoeba histolytica. In about 10-20% of the people it infects, this parasite inflames cells and destroys tissues in the intestines, a condition termed amoebic dysentery.
But everyone knows bacteria cause gum disease, so for a long time, Entamoeba was thought to more or less be lurking.
Then it was discovered that in inflamed gingival pockets, the amoeba’s protein-manufacturing equipment was second in abundance only to the human form. That inspired some understandable nervousness and a more concerted investigation.
Now the German scientists at the university hospital Charité – Universitätsmedizin Berlin who conducted that investigation have published their findings in the May issue of the Journal of Dental Research and have evidence that these amoebas are doing much more than lurking: they appear to suck the hearts right out of our cells.
You can see it happen in the video below. The amoeba is the light gray cell in the center, surrounded by wriggling skinny cells that appear to be bacteria. The cell it's attacking is at upper left, and the dark blob being sucked into the rear end of the amoeba at upper left is its nucleus, the compartment where the DNA is kept. The amoeba crawls to the right and down, sucking nucleus all the while. The host nucleus is visibly smaller at the end of the video.
Credit: Mark Bonner dmd Institut International de Parodontie, Wikimedia (CC BY-SA 3.0)
In this particular series of experiments, the scientists found that in people with severe gum disease, 77% of the inflamed gum sites contained this amoeba, while only 22% of healthy tissues in the same mouths did so.
Next, the scientists took tissue samples from the gums of people with severe periodontitis and looked at them under the microscope. They found amoebas surrounded by lots of white blood cells called neutrophils.
E. gingivalis seem to have a particular fondness for the nucleus of gum surface cells and neutrophils. They even seem to bait the immune cells by provoking the gums to secrete a molecule called interleukin 8 (an inflammatory cytokine) that summons neutrophils. The scientists found that host tissues increase their production of this chemical a resounding 1,900 times in response to the amoeba, a level comparable to that seen in the gut of people with amoebic dysentery.
Could the amoeba invade on its own? When the team exposed tiny pieces of healthy gum tissue to the amoeba for six hours, it couldn’t get in. But when they slightly sliced or punctured the healthy gums, it easily slipped inside. Within six hours, amoebas had already shoved their pseudopods into gum cells and were busy swallowing pieces of nuclei like kids clutching broken cookie jars. As in the video above, the scientists could actually see DNA being sucked inside.
Next, they tested the biochemical response of gum tissue cells to E. gingivalis, and discovered the amoeba seems to invade and destroy tissues in ways very similar to E. histolytica. In addition to juicing interleukin 8 signaling, it also causes host cells to pump out lots of a biochemical called host matrix metalloproteinase 13 that breaks down the protective goo coating that encases our gums. This molecule is normally involved in wound healing, tissue remodeling, cartilage degradation, bone mineralization, and ossification, but in the context of periodontal disease it is a sign of invasion, destruction and inflammation, the scientists say.
Moreover, gut surface cells exposed to E. histolytica react by committing suicide. In this study, the scientists observed that gum surface cells exposed to E. gingivalis seemed to react the same way.
The authors conclude that the amoeba can no longer be regarded as an opportunist, but as a pathogen.
On the other hand, becoming infected by the amoeba by no means means that you will develop disease. In this study, 15% of healthy controls unaffected by gum disease still harbored Entamoeba gingivalis in their mouths. In these cases, the amoeba truly appeared to be lurking.
Of course, this is just one study, and it has yet to be replicated. But given the prevalence of gum disease, I think it's important food for thought, because the implications are pretty serious.
The creepiest is perhaps that E. gingivalis can spread between people by some of the same infamous respiratory droplets (along with kissing and sharing eating utensils) that have so recently gripped our attention thanks to COVID-19. Obviously, amoebas are much, much bigger than viruses, which means that it probably requires much bigger and therefore rarer droplets for them to spread. But the fact that aerial (and mouth to mouth) transmission is an option for a presumptive gum disease pathogen is a real eye opener to me.
Secondly, in amoebic dysentery, E. histolytica damages tissue such that intestinal bacteria can invade the body cavity and may find their way to other organs, initiating or complicating other diseases. Gingivitis and periodontal disease also seem to exacerbate diabetes, cardiovascular disease, rheumatoid arthritis, cancer, pneumonia, and even premature birth and low birthweight. Could bacteria that invade the body from the mouth be involved, and could an amoeba be the one letting them in?
Finally, Entamoebas are not easy to evict. Many species are resistant to antibiotics, antimicrobial peptides and (obviously) neutrophils. In serious cases of periodontal disease, it may be a formidable and underestimated opponent. The authors conclude by suggesting dentists ensure they clear the pathogen from the gums of periodontal disease patients they are treating. At least one large periodontal practice in France and Quebec claims to have developed a method that does so.
For you as the potential patient, however, the take away is a little different. Brushing and flossing are a drag, sure. But you have to ask yourself whether the alternative is worse. Given the increasingly strong links between gum disease and other chronic disease, not to mention the potential for the slithering vampiric amoebae running amok, I think the answer is a resounding YES.
Bao, X., R. Wiehe, H. Dommisch, and A. S. Schaefer. "Entamoeba gingivalis Causes Oral Inflammation and Tissue Destruction." Journal of Dental Research 99, no. 5 (2020): 561-567.