When we stop to consider what our greater purpose is in life, we often do not think of ourselves as host to trillions of bacteria. We may always take comfort in the fact that numerous bacterial species could not exist without our assistance. This relationship, however, is mutual. We depend on them for many important functions in our daily lives. Bacterial cells outnumber our cells in a ratio of approximately ten to one, and they are most prevalent in the digestive tract. The many bacterial populations in our bodies exist in a balance with each other. As long as they are not disturbed, this natural balance is beneficial, particularly to our digestion. When foreign bacteria are introduced or other events occur to disrupt the natural populations, there are harmful effects. Altered bacterial population ratios have been indicated as markers for digestive tract illnesses and metabolic disorders, including obesity and diabetes.
The two most abundant bacterial populations in our digestive system are bacteriodetes and firmicutes. In digestive tract illnesses, such as inflammatory bowel disease or irritable bowel syndrome, the number of firmicutes is abnormally high. Similarly, obese individuals and people with type 2 diabetes also exhibit high levels of firmicutes. It remains unclear, to my knowledge, whether these findings are correlative or causative, but they at least provide an interesting marker for diseases involving our digestive system. Now, one might think to simply cultivate a higher number of bacteriodetes or to design a treatment that specifically kills firmicutes. Unfortunately, the human microbiome is more complicated than that, and studies attempting this approach have found that an abnormally high bacteriodetes population relative to firmicute population is also detrimental to our health.
Microbiome studies have also revealed that mice with no bacteria in their guts respond much slower to changes in diet. When placed on a high fat diet, their weight barely changed. This indicates the importance of bacteria in extracting nutrients from food, and provides valuable information on the importance of balancing bacterial populations rather than destroying them. Our usual approach to infections are to prescribe lots of antibiotics. Antibiotics are a simple solution to bacterial infections, and often times a necessary one to address the immediate problem. However, they often come with side effects due to the widespread destruction of beneficial bacterial populations. Additionally, the use of antibiotics in children can disrupt the development of their immune systems. I am not advocating for the avoidance of antibiotics. That would be almost as ridiculous as avoiding vaccinations. Antibiotics treat the immediate and most dangerous issue. They are very necessary. That being said, the human microbiome has many intricate interactions that we will need to understand and respect as we continue to develop our medical knowledge.
Currently, we have two means of modulating the bacterial populations without outright killing them. The first is the most commonly known: probiotics. They are population dietary supplements and often recommended after antibiotic treatments. Probiotics contain living microorganisms that can colonize an individual’s digestive tract and provide health benefits. The second method is far less glamorous: fecal microbial transplantations. This method involves transferring fecal bacteria from a healthy individual to a patient with abnormal microbial populations. It is often used following a C. difficile infection because the antibiotics required to treat a C. difficile infection are extremely harsh. Because of the differences in bacterial populations between healthy and obese individuals, it may be possible in the future to attempt a fecal transplant from a healthy individual into an obese individual. We will need a greater understanding of whether the differences in bacterial populations are correlative or causative before we consider this as a viable means of reducing obesity.
The human microbiome is a fascinating and active area of research. There are numerous benefits to increasing our understanding of the bacterial cells that share our bodies. We are far from being able to prescribe probiotic or antibiotic treatment courses to address metabolic diseases, but we are beginning to understand the microbiome level interactions involved. It has taken centuries of research to understand the interactions between our own cells, the ones outnumbered ten to one by bacterial cells in our own bodies. It may take some time to fully understand bacterial populations, but the information will provide us with a more complete understanding of disease causes, treatments, and methods of prevention.