In my early days in the clinical laboratory, it was thought that, other than the gut, the body’s organs were normally sterile. Infections in the brain were rare and only seen in cases of meningitis, encephalitis, or central nervous system wounds. Now, with the ability to search for microbes using genetic testing it’s well known that many organisms can find their way into the brain. In Alzheimer’s disease, the brain commonly contains microbes, particularly viruses, bacteria, fungi and protozoa. Age-matched controls from subjects without Alzheimer’s disease can, to a lesser extent, also harbor these microbes. This article describes microbes, the microbiome and the ways in which these microorganisms enter the brain.
Microbes and the Microbiome
Trillions of microbes, primarily bacteria, co-exist with man. Genetic studies confirm that the human body contains more bacterial cells than human cells. The microbiota, which is sometimes referred to as the microbiome, is an individual’s unique ecological community of microorganisms found inside, on and around all multicellular organisms, including animals and plants. Microbes have their own DNA, and the microbial genetic material present in a person’s body is referred to as their microbiome. In families, most family members have similar microbiomes.
Many of the microorganisms that we harbor are commensal, meaning that they benefit us, for instance the gut microbes that help infants digest the sugars in breast milk that would ordinarily be harmful. Microbes can also be parasitic, using us for their survival, or they can be pathogenic, causing disease. While microbes inhabit every inch of the body, they’re most abundant in the colon. The human colon contains 10-100 trillion microbes including thousands of different bacterial strains that collectively weigh between two and five pounds. The types and amounts of the various gut microbes in an individual are affected by diet, antibiotic use, the environment, pesticides, countries visited, and even our family pets.
Microbes in the colon help us digest foods, remove toxins, and synthesize a variety of biochemicals, including hormones, lipids, clotting factors, neurotransmitters, and vitamins. The gut microbiota is usually composed of the same basic microbes in a given population although differences associated with various diseases frequently occur. Our gut microbes also manage to ingest medications and dietary supplements, causing discrepancies in the effects of a therapeutic drug dosage, especially when changes to the normal microbiota exist.
In particular, in Alzheimer’s disease the gut microbiota is markedly different with far less diversity and significantly fewer Firmicutes, Actinobacteria, and Bifidobacterium species and marked increases in Bacteriodetes than the microbiota seen in the normal population. In addition, in people with type 2 diabetes, increased blood levels of bacterial 16SrDNA from gut bacteria are seen long before the disease develops. In some diseases such as Parkinson’s, the short chain fatty acids produced by gram negative microbes such as Escherichia coli have been found to cause the characteristic protein misfolding that damages neurons in this disease.
Gut Dysbiosis and Leaky Gut Syndrome
Imbalances and alterations in the microbes that inhabit the gastrointestinal tract cause conditions of gut dysbiosis. Dietary changes, especially an increase in fats, and the use of antibiotics can cause significant changes in the gut flora within a few days. Conditions of dysbiosis, along with viral infections, are known to cause chronic infection, gastrointestinal cancers, mental and psychological disorders. The associated chronic inflammation results in the characteristic pathological changes seen in obesity, diabetes mellitus and Alzheimer’s disease.
The lining of the gut can also be injured by certain medications including proton pump inhibitors and non-steroidal anti-inflammatory drugs causing a condition called leaky gut syndrome. In leaky gut syndrome, which causes symptoms of mental fog, diarrhea, sugar cravings, and fatigue, biochemicals and microbes can cross the normal barrier and make their way into the central nervous system. Vascular changes can also result in damage to the blood brain barrier, facilitating the passage of these substances into the brain. The chronic inflammation caused by leaky gut syndrome and in diseases that injure the blood brain barrier has found to be identical to the chronic inflammation seen in Alzheimer’s disease.
Protecting the Brain
In Alzheimer’s disease plaques of amyloid beta protein that lodge between neurons interfere with the brain’s normal signaling systems. Unable to communicate with one another cells are unable to form memories. In the last decade researchers have learned that amyloid beta protein is an antimicrobial substance that is produced in response to infection. Postmortem brain studies show that this protein is found in individuals with normal cognition, in moderate amounts in Parkinson’s and other neurological disorders, and in much higher amounts in the brain of individuals with Alzheimer’s disease. Various studies have also shown the presence of significant numbers of viruses, bacteria, fungi or protozoa in the Alzheimer’s brain. While no one microbe is responsible for the production of amyloid beta protein and chronic inflammation seen in Alzheimer’s disease, a clear link to infection, particularly infection with Herpes viruses, has been demonstrated in Alzheimer’s disease.
Various studies have focused on healing chronic infections and chronic inflammation by using good dental hygiene, treating chronic infections, healing mitochondrial dysfunction, and treating vascular disease. Avoiding nonsteroidal anti-inflammatory medications, glyphosphates used as pesticides, GMO foods, drugs for constipation such as MiraLax, and food allergens also offers benefits in preserving the gut lining.
Dietary supplements known to heal leaky gut syndrome and protect the brain include marshmallow root, slippery elm, quercetin, bromelain, licorice root extract, and grape seed extract.
While protecting and healing the gut microbiome benefits numerous gastrointestinal disorders, the use of fecal microbe transplants is now used as a therapy in multiple sclerosis and other autoimmune disorders and in Clostridium difficile infection. In cases of marked dysbiosis restoring the gut microbiota can bring dramatic changes. Today, any companies use a process of metatranscriptomics to identify the predominant gastrointesinal organisms to develop health assessments and recommendations. If this seems extreme, one can add more fermented foods, which are loaded with beneficial microbes, to help restore a healthy balance.