Before we leave a public bathroom, how many times do we see or hear the phrase, “Did you wash your hands?” Chances are, we have seen or heard this plenty of times. As children, we were often reminded by our parents to wash our hands before and after eating, after handling dirty items, or after going to the bathroom. The obvious reason is to eliminate the germs that we have come into contact with throughout the day. However, as we all know, bacteria are not entirely harmful to our well-being. In fact, some bacteria in our gut function to keep us healthy. They help digest food, aid us in acquiring vitamins and nutrients, train our immune system, and compete with pathogenic bacteria that may otherwise be harmful to us. As such, they are called commensal microorganisms. Certain diseases caused by pathogenic bacteria are treated by a process called fecal matter transplant. This medical procedure involves the introduction of the normal gut flora obtained from the stool of a healthy donor in order to restore the gut microbiota of the infected individual. The concept behind this procedure is that the commensal microorganisms obtained from the stool will eventually outcompete the pathogenic bacteria responsible for the disease. For example, Pseudomembranous colitis, which is caused by Clostridium difficile, uses fecal matter transplant as one feasible treatment option. In the process, non-pathogenic bacteria are introduced into the colon of the patient in order to outcompete C. difficile for resources. However, is the commensal microbiota as beneficial as it is portrayed? Studies aimed towards understanding the pathology of multiple sclerosis (MS) would beg to differ.
MS is an autoimmune disorder of the central nervous system (CNS) where the myelin sheath, which wraps around the axon and facilitates the conduction of nerve signaling, is attacked by the immune system. The resulting demyelination causes signals between neurons to be delayed and this consequence is manifested through clinical symptoms that include numbness, motor dysfunction, and vision problems. In terms of the immune response, MS is mostly associated with increased CD4+ T cell infiltration into the CNS. This T cell infiltration is also accompanied by increased production of autoantibodies by B cells, which can attack the specific myelin proteins that make up the myelin sheaths. Several studies are aimed towards understanding what goes awry in MS, however, numerous questions remain unanswered regarding this disorder. Microbial infection has been attributed to this autoimmune disorder (Ascherio et al. 2007). As mentioned earlier, the commensal microbiota has been linked to the treatment of certain diseases by outcompeting pathogenic microorganisms. Therefore, could the microbiota also play a role in treating MS? A recent study shows that in the case of MS, commensal microbiota triggered autoimmune demyelination instead of alleviating MS symptoms.
