On every scale of human interactions, be it a small gathering of people or a United Nations meeting, we divide mankind into friends, strangers or enemies. In the same way, our immune system discriminates the “micro” world that it comes into contact with. The body’s own components are viewed as friendly, but unknown or foreign structures are treated with suspicion and will evoke a response. Known enemies, however, will trigger a strong immune response to get rid of the irritant.
Our immune system, however, has to deal with the microbes that colonise our digestive tracts and there are trillions of these organisms. In fact, the body contains 10 times more foreign microbial cells than our own body cells, making us only one tenth human! These organisms are critical to our well-being by executing essential functions: digestion of our food, processing and exchanging nutrients, protection against infection. It would be impossible to live without them.
The truly friendly species are tolerated, even fostered by the immune system. Bacteria support the development and maintenance of the immune system and in turn the immune system helps protect these species from other less friendly invaders. It’s a win-win situation. We should love these little guys.
Here are 39 things you may not have known about your gut bacteria:
- The average body contains about 100 trillion symbiotic bacteria, outnumbering host cells by a factor of 10.
- These organisms express 10 fold more unique genes than their host’s genome.
- The expression of genes from these organisms affects our body function in measurable ways.
- The highest number of immune cells reside at sites colonised by these organisms.
- Antibiotic use, changes in diet and elimination of prebiotic foods have resulted in higher rates of allergies in developed countries, as well as auto-immune and inflammatory disorders.
- Complex communities of bacteria keep one another in check. The same species can be beneficial or damaging depending on the environment they find themselves in. I guess that is the same for human behaviour.
- Under normal conditions, the gut of a fetus is thought to be sterile and the first exposure to microorganisms occur through the vaginal tract of the birth canal and subsequently the breast milk (and colostrum) of the mother. It is for this reason that both C-section births and bottle-feeding are linked to higher allergy rates in children.
- The early colonization just after birth sets the stage for the development of the immune system in the long-term. The baby’s immune system is learning who are friends, strangers and enemies and this early information is critical for responses that the baby will bear for a lifetime.
- Antibiotic use in mothers prior to pregnancy will negatively impact on the immune development of their children.
- Recovery of the microbiota after antibiotic use can take 6 – 12 months and some critical species may never recover. Antibiotics should be very carefully considered – especially in women planning to conceive.
- One specific type of bacteria has been directly shown to protect against colitis in mice, human studies are under way.
- Research shows that early exposure to friendly microbes reduces the person’s risk of developing inflammatory diseases later in life.
- Studies performed in animals raised in the absences of live microbes (germ-free sterile environments) show that the immune system of these mice have dysregulated responses leading to ailments such as asthma.
- The same studies showed that these mice are susceptible to infection when placed back into a normal environment.
- The microbial communities signal our immune cells when enemy bugs invade and play a critical role in protecting us from infection.
- Our microbial friends produce chemicals that maintain the tight junctions (or gaps). Like the Great Wall of China, the gut wall has access points at certain intervals that control which substances will be allowed through the border (friends, enemies or strangers). When these tight junctions break down, larger molecules breach the body’s defenses resulting in an immune attack on otherwise innocuous substances (such as foods). The result is food allergies to even healthy foods.
- The microbial populations regulate pathways that support a myriad of body functions. Failure of this regulation leads to inflammatory bowel disease, allergies, auto-immune conditions and metabolic syndrome.
- The bacterial-induced suppression of inflammation is not only limited to the gut. The site of inflammation may be experienced far from the gut. Arthritis for instance, is an inflammatory response that results from the gut.
- Good bacteria prevent the growth of harmful species by both producing antibacterial substances and signals to alert our own immune cells to intruders.
- Human studies have shown that broad-spectrum antibiotic treatment can allow domination of drug-resistant microbes that cause serious infection.
- Infections caused by multidrug-resistant bugs are on the rise.
- Studies show that the most effective treatment for colitis caused by Clostridium difficile is by replacing healthy bacteria.
- One study showed that reduction of healthy bacteria after antibiotic treatment made individuals more susceptible to influenza and pneumonia. The same individuals showed lower levels of active immune components being created.
- Certain chemotherapy drugs destroy bacterial communities and lower resistance in patients being treated for cancer.
- Germ free mice (mice in which all bacteria are absent) show much higher incidence of tumours.
- Both Crohn’s disease and ulcerative colitis (UC) are associated with genes that are critical in maintenance of the gut barrier and regulation of the immune response. In both conditions the complexity of the gut communities are markedly reduced.
- Crohn’s disease is associated with bugs that create inflammation including Yersinia and Clostridium. These bugs subvert our own immune responses to generate response to healthy bacteria and even benign foods.
- Some bacteria thrive in inflammatory conditions, using the nitrate by-products to survive, skewing the healthy balance even more.
- Transferring the gut bacteria of mice with ulcerative colitis to other mice results in the recipients also developing colitis and subsequent colonic cancer.
- Genetic sequencing of patients with Rheumatoid Arthritis shows the prevalence of specific inflammatory-inducing bacterial species. Researchers can control the development of RA in mice by manipulating their gut bacteria.
- In mice, researchers have been able to induce multiple sclerosis (MS) by altering gut bacteria. For years researchers have known that the disease varied among genetically identical animals housed in different settings.
- Gut bacteria provide protection against some inflammatory disorders including type 1 diabetes.
- In animal studies, mothers passed on immunity against certain disease through passing on their microbial communities.
- Liver and Intestinal cancer is inextricably linked to inflammation in the GI tract.
- Microbiota has been shown to play an important role in the development of metabolic syndrome and Type 2 diabetes, with altered communities resulting in an altered metabolism of the host.
- In mice, the above conditions are transferrable – simply by inoculating healthy mice with the gut bacteria of the ill mice.
- Mice that do not have certain species of gut bacteria grow obese faster than mice with healthy gut bacteria.
- The gut bacteria are very sensitive to changes in diet. For instance, cruciferous vegetables contain components that signal important immune responses.
- Mice fed high saturated fat diets have altered gut communities that effect energy production and immunity.