By: Dr. Caitlin Vonderohe
Researchers and clinicians of both human and veterinary medicine are constantly seeking to understand and use the microbiome as a diagnostic tool, a clinical therapeutic target and a means to improve health and growth performance. Professor Mark Lyte discussed the current efforts to understand the microbiome, the challenges of studying populations of bacteria in a living host, and a valuable perspective on the future of this research in a presentation entitled “Microbial endocrinology: Why integration of microbiology, neurobiology and nutrition matters to overall health and behavior in pigs” at the 14th International Digestive Physiology of Pigs Symposium in Brisbane, Australia.
One of the great challenges of microbiome research is the fact that the microbes living in the gut live in communities that interact with each other, and interact with the host. These communities may change in composition or function in states of stress or quiescence, which may, or may not, be detectable with sequencing technology. Small changes in microbial populations may be indicative of dramatic changes in physiologic state or health, while a large shift in population may be an incidental finding. These changes are governed by host-microbial community interactions.
Microbial endocrinology is the union of microbiology and neurology, and represents the great evolutionary link between microbiome communities and the host. Animals rely on neuroendocrine molecules such as hormones and neurotransmitters to relay messages between cells. The same neuroendocrine molecules are used and produced by bacteria, but also found in foods and feed ingredients. For example, when Y. enterocolitica was treated with nanomolar concentrations of norepinephrine, it became 50,000 times more infective. Staphylococcus epidermidis grows faster and forms biofilms in the presence of norepinephrine. Campylobacter jejuni, a normally micro-aerophyllic organism, becomes aerotoloerant in the presence of norepinephrine.
The simple fact that bacteria produce and respond to the same neurosensory molecules as humans and pigs indicates the microbial community-host interaction can be bidirectional. This is complicated and exacerbated by the gut as a primary producer of norepinephrine and dopamine, and foods and feed ingredients also contain the same compounds. The enteric nervous system runs the length of the gastrointestinal tract, from the basal muscle to the tip of the villi and represents part of the bidirectional flow of information from the microbial communities in the gut to the brain. This communication is so sensitive, that when a mouse intestine is colonized by a nonpathogenic bacteria, it is strongly associated with increases in anxiety-like behaviors in the mouse. Nutrition significantly affects the gut-brain-microbe interaction. Feeding animal protein to stressed mice alleviated the cognitive issues (inability to complete a maze) associated with stress.
At this point in time, the understanding of the microbiome, and the ways the microbiome can be studied, are not sufficient to efficiently use the microbiome as a diagnostic tool or clinical target for therapy. According to Professor Lyte, in order for this field to progress, the scientific community needs to focus on the mechanisms of microbiome-host interactions. Research dating to the 1930’s has shown that the microbiome interacts with the brain. The enteric nervous system interacts with the microbiome and the immune system in the gut. It will be important to better understand these interactions, and their physiologic and health-related effects to be able to use the microbiome as a diagnostic tool or therapeutic target.