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Gut Instinct

New research details the relationship between microbiota and the eye. Here’s what you should know.
By Joseph P. Shovlin, OD

11/15/2017

If you were to pick up any professional medical journal today, you would likely find a discussion on microbiota’s relationship with diseases and their pathogenicity. In many parts of the body—including the eye—a normal community of bacteria and micro-organisms helps confer resistance to infection.1-6 Literature suggests the gastrointestinal (GI) microbiome is associated with host health status and its structure and composition define functional gene expression, pathogen abundance and overall host response. 

A recent investigation of oral microbiota shows a possible connection to glaucoma. Patients who have glaucoma seem to have higher quantities of oral bacteria than controls without glaucoma.7

Striking a Balance
A significant body of evidence suggests GI microbiota may define states of health and disease in a complex manner. Strategies to improve host health, including the ocular health, may rely heavily on manipulating the delicate balance of this ecosystem.1 Specifically, the host community must provide balance between maintaining a favorable environment while protecting against invasion or outgrowth of pathogenic species of microbes.1 Prenatal and postnatal exposures allow the immune system to develop the ability to discriminate between harmful and beneficial microbial species.1,2,5

Recent studies have provided evidence of a link between early GI colonization events in those under a year of age and subsequent development of allergic disease.1 Microbiome deviations at an early age may be associated with immune disease. Studies also show that antibiotic use in infants could change the gut microbiota, which may adversely impact the immune system and increase the risk of atopy in specific groups of children.5

Disruption of the microbiome in the adult gut is also associated with many diseases and appears to be characteristic of various chronic inflammatory diseases.1 The use of antibiotics has raised concerns for the potential adverse affects on gut microbiota by impacting the native microbial community.1 Introducing pathogens orally through diet provides individual host and micorobiota variability, directly affecting the dynamic ecosystem.2

Host resistance to certain infections may be altered by commensal organisms prior to infection occurrence. In herpes simplex, for example, microbiota may enhance, reduce or have no substantive effect on a viral infection, depending on the host response.2 The influences on an infection may be by direct mechanisms such as virion modification, or indirect mechanisms such as host cell modification.1,2,4 Conversely, microbial products can indirectly enhance viral replication and herpetic disease.2

Probiotics and prebiotics represent some promise for inflammatory disease management by promoting subsets of existing GI bacterial community members capable of degrading and increasing the production of anti-inflammatory compounds.6

Ocular Surface Stability
Conjunctival diversity of bacteria is actually greater than that of the skin, and the direct impact of contact lens wear on the ecosystem is yet to determined. Host commensal bacteria of the ocular surface interacts with the host immunity to suppress microbial pathogenicity. Manipulation of the microbiome through pro-, pre- and symbiotic supplementation may prove an attractive alternative for improving host health status that might specifically include the eye.1,4

Leveraging the role of our microbiota in infections to alter the course of certain infectious diseases may be a reality someday. However, it will require a better mechanistic understanding of microbiota function and a more comprehensive knowledge of how microbes affect resistance and susceptibility to various pathogens.1,2,4 Will we someday prescribe specific novel supplementation for contact lens wearers to help safeguard against infection or help control inflammation? Perhaps, because human biology and health are  inter-related due to the influences of our microbial inhabitants.   

1. Fujimura KE, Slusher NA, Cabana MD, Lynch SV. Role of the gut microbiota in defining human health. Expert Rev Infect Ther. 2010;8(4):435-54.
2. Pfeiffer JK, Sonnenburg JL. The intestinal microbiota and viral susceptibility. Front Microbiol. 2011;2:92.
3. Dreyfus DH. Herpesviruses and the microbiome. J Allergy Clin Immunol. 2013;132(6):1278-86.
4. Shin H, Price K, Albert L, et al. Changes in the eye microbiota associated with contact lens wearing. mBio. 2016;7(2):e00198-16.
5. Johnson CC, Ownby DR, Alford SH, et al. Antibiotic exposure in early infancy and risk for childhood atopy. J Allergy Clin Immunol. 2005;115(6):1218-24.
6. Lewis S, Brazier J, Beard D, et al. Effects of metronidazole and oligofructose on fecal concentrations of sulphate-reducing bacteria and their activity in human volunteers. Scand J Gastroenterol. 2008;43(11):1346-52.
7. Lu JL, Liu J. Human microbiota and ophthalmic disease. Yale J Biol Med. 2016;89(3):325-30.


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