Breaking down the microbiology world one bite at a time
Keeping an eye for the gut microbiota!
The gut microbiota is the entirety of the gut microorganisms which not only include bacteria but also viruses, fungi, and archaea. In a healthy human body, despite individual differences (due to environment, dietary habits, or the intensity of physical activity of each individual) we find similar microbes.
The gut microbiota is essential to ensure the proper functioning of the human body. When everything is going well, microorganisms help each other as well as their human host, it’s called symbiosis. Yet sometimes an imbalance in the microbiome (called dysbiosis) can occur. Some dysbiosis are the result of an underlying disease, others are the cause of a new disease, and in some cases, we still don’t know which one from the dysbiosis or the disease came first.
This exciting subject of the gut microbiota is being studied more and more and regularly a new link to another body part, another disease or imbalance is found. But today we will talk about a body part quite far away from the gut: the eye!
Many eye diseases threaten our sight, whether they result in discomfort (itching due to conjunctivitis), decreased visual acuity, or blindness (total loss of sight). One of the most common eye diseases is dry eye disease (DED). This disease is characterized by a decrease in quantity or quality of tears resulting in stinging sensation and eye discomfort. In the majority of cases, DED is linked to aging with 15% of people aged over 60 suffering from this disease.
There is already a known link between aging and gut microbiota deterioration, especially with a decrease of microorganisms diversity, therefore a link between dysbiosis and emergence of DED is quite a plausible hypothesis. And to test this hypothesis, Yoon and colleagues studied mice populations of different ages: 8 weeks, 1 year and 2 years. They looked at both the evolution of their eyes and their gut microbiota. To do so, they observed the microbiota diversity by identifying bacterial populations in their feces and the dryness of their eyes by monitoring the quantity of their tears. The authors found correlations between microbial imbalance (dysbiosis) and the severity of DED.
As shown in the figure, the oldest mice had the most severe DED and the least diverse microbiota which lead us to assume a link between the two.
However, due to the small number of subjects in the study (fifteen of 8 weeks old, ten of 1 year old, and only eight of 2 years old), this study only shows preliminary results paving the way for other studies, especially directly in humans. There are still a lot of parameters to take into account before being able to conclude on a definite link between gut microbiota and DED. However, these first results are promising and could maybe one day allow us to cure DED with probiotics: repairing a microbiota imbalance by adding missing “good” bacteria could decrease the severity of DED.
Link to the original post: Yoon, C.H., Ryu, J.S., Moon, J. et al. Association between aging-dependent gut microbiome dysbiosis and dry eye severity in C57BL/6 male mouse model: a pilot study. BMC Microbiol 21, 106 (2021).
Featured image: Combination of 2 pictures
https://pixabay.com/illustrations/bacteria-medical-biology-health-3662695/
https://commons.wikimedia.org/wiki/File:Human_eye_with_blood_vessels.jpeg
micro-bites.org 
