Microbiome: The sinister enviroment

The estimate for the ratio of living bacteria to cells in our body is 1:1. Approximately 30 trillion bacteria to 30 trillion cells, to be exact. The microbes in or on the body are known as the human microbiome. Exposure to microbes occurs at birth, but the microbiome of each individual varies greatly and is influenced by environmental factors such as diet, behavior, and exposure to antibiotics.

This microbiome can influence health and disease. Some microbes aid in digestion and support the immune system, while a disturbance or dysbiosis of the microbiome has been shown to promote disease. Ninety percent of the body’s microbial mass exists in the gut.

Understanding how the microbiome influences health is an exploding area. A recent Google search of the word microbiome yielded almost six million results. Dysbiosis, an imbalance in the microbiome, has been linked to several diseases, including inflammatory bowel disease, irritable bowel syndrome, obesity, type 2 diabetes, and autism.1 Disruption of homeostasis in the microbiome of the body and in oral biofilms have “disease promotion” in common. Interestingly, dysbiosis in pathogenic biofilm within the oral cavity creates microcosms that foster inflammation and promote formation of pathogenic bacteria implicated in numerous systemic diseases.

In 2016, NYU Langone Medical Center researchers discovered that people with the oral microbiome including P. gingivalis have a 59% greater risk of developing pancreatic cancer compared to those who do not have it. Those with A. actinomycetemcomitans have a 50% greater risk of pancreatic cancer.2 In August of 2017, data linked P. gingivalis that thrives in pathogenic biofilm to increased risk of rheumatoid arthritis.3 Last year, researchers found that people whose esophageal tumors tested positive for F. nucleatum have poorer survival outcomes compared to those who did not have F. nucleatum.4

These sobering facts should encourage every dental professional to view bleeding gums that breed pathogenic biofilm differently. It is a sinister environment that promotes disease. Period.

Gut microbiome and cancer

The gut microbiome has also recently been tied to increased risks of cancer. H. pylori infections are common, and the Centers for Disease Control and Prevention (CDC) estimate that two-thirds of the population carries the bacteria.5 H. pylori can spread through food contamination and mouth-to-mouth contact. Once inside the host, H. pylori burrow into the mucous layer that lines the stomach, making it difficult for the host’s immune response to recognize it. For susceptible individuals, the development of an H. pylori infection increases the risk for ulcers and gastric cancer due to the insult of chronic inflammation.

F. nucleatum is found in both healthy and diseased mouths but seems to thrive in oral biofilms that are imbalanced, and this warrants our attention. F. nucleatum is also a player in the gut microbiome linked to colorectal cancer. F. nucleatum has been found in colorectal adenomas and advanced-stage colorectal cancer.6 Evidently, this pathogen induces an inflammatory response and activation of cancer-promoting genes, which in turn increases the rate of proliferation of colorectal cells.

That’s not all. F. nucleatum orchestrates a molecular network that increases chemo-resistance, thereby making the recurrence of colorectal cancer more likely.7 Additionally, research has shown that cancer can develop in a healthy mouse after transferring the microbiome via a fecal transplant from another mouse with colorectal cancer. We certainly need to be cautious as not all animal studies yield the same results in humans, yet increasing evidence indicates a key role for the bacterial microbiota in carcinogenesis.

Gut microbiome and immunotherapy

Gut microbiome has emerged as an interesting target for improved cancer therapies. Researchers from the MD Anderson Cancer Center recently did sequencing on the gut and oral microbiomes for patients with melanoma.8 While there were no significant differences in the oral microbiome of melanoma patients, lead researcher Dr. Jennifer Wargo found patients with diverse gut microbiomes fare better with chemo than patients with fewer types of gut bacteria. Her study builds on a growing hypothesis that altering gut microbiome might improve a person’s response to immunotherapies.

At the end of 2016, a phase 2 clinical study at Roswell Park Cancer Institute became one of the first human trials that will look for links between the microbiome and the response to immunotherapies. The trial will analyze how 40 ovarian cancer patients respond to a combination treatment of an immunotherapy drug and two other cancer drugs, and then it will evaluate the blood, tumor, stool, vaginal, and skin microbiomes to identify any associations with clinical outcomes and tumor responses. For those exploring drug responses and searching for improved outcomes, altering the microbiome may become a new frontier.

We should all stay tuned to the science surrounding the human microbiome and invest in dietary and lifestyle choices that foster a healthy gut microbiome and healthy oral microbiome.

Karen Davis,RDH, BSDH, is the founder of Cutting Edge Concepts, an international continuing education company, and practices dental hygiene in Dallas, Texas. She is an independent consultant to the Philips Corp., Periosciences, and Hu-Friedy/EMS. She can be reached at [email protected].

References

1 Cho I, Blaser MJ. The human microbiome: At the interface of health and disease. Nature Reviews: Genetics. 2012;13(4):260-270.

2 Jacob JA. Study links periodontal bacteria to pancreatic cancer risk. JAMA. 2016; 315(24):2653-2654.

3 Potempa J, Mydel P, Koziel J. The case for periodontitis in the pathogenesis of rheumatoid arthritis. Nature Reviews: Rheumatology. 2017.(10) 606-620.

4 Yamamura K, et al. Human microbiome fusobacterium nucleatum in esophageal cancer tissue is associated with prognosis. Clinical Cancer Research. 2016; 22(22): 5574-5581.

5 Helicobacter pylori and cancer. National Cancer Institute website. www.cancer.gov. Accessed November 13, 2017.

6 Han YW. Fusobacterium nucleatum: a commensal-turned pathogen. Current Opinion of Microbiology. 2015;23:141-147.

7Nosho K, et al. Association of Fusobacterium nucleatum with immunity and molecular alterations in colorectal cancer. World Journal of Gastroenterology. 2016; 22: 557-566.

8 The microbiome and cancer: what’s all the fuss about? Cancer research UK website. www.cancerresearchuk.org. Accessed November 13, 2017.