The microbiota ecosystem is an important determinant of human health. Recent findings suggest several connections between microbiome composition and the onset and treatment of certain diseases. The following paper presents a summary of available information on principles of microbiota composition, its relation to the immune system, and possible implications for the healthcare process.
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Recent findings in microbiology suggest that the composition of the human microbiome has a significant effect on an individual’s state of health. More importantly, it has been determined that microbiome composition varies depending on several factors, including geographical location and the functions of a body part. Therefore, it would be logical to suggest that individual and group differences in microbiome composition determine the effects of microbiota on human health. The first factor that is considered responsible for the observed differences in the functional properties of the site where the microbiota proliferates. For example, the composition of a bacterial community within a microbiome occurring in the oral cavity is expected to be relatively similar in different individuals (Clemente et al. 1258). However, it is also evident that despite the similarities, communities in different hosts display significant inter-individual variability.
While some of the differences can be attributed solely to individual parameters, certain demographic factors are also known to influence the outcome. For instance, the microbiome found in infants differs significantly from that occurring in adults (Dave et al. 249). In a similar manner, gender differences are also associated with a certain amount of variety in microbiome composition. On a larger scale, human groups such as populations of a certain ethnicity may harbor a microbiome with a unique set of characteristics. The most apparent explanation for the phenomenon is the involvement of genetic variables, which would also account for the differences between individuals within a given ethnic group. Several researchers point to the fact that microbiota from related individuals living in the same environment features more similarities than those found in unrelated people, confirming the assumption (Goodrich et al. 789). However, it is also reasonable to consider environmental factors as responsible for at least some of the similarities.
The factors that affect differences in community microbiome composition can be divided into two categories. The first category focuses on environmental factors and includes diet, gastrointestinal infections, smoking, and the effects of medications, with antibiotics having a major impact on community microbiome composition. It should be pointed out that the environmental factors that likely affect the microbiome are numerous, complex, and, as a result, difficult to control. For this reason, the available findings are inconclusive. Nevertheless, it has been established that only 10% of the microbiota remains unchanged over a long period of time, which suggests that the majority of changes are determined by external influences (Dave et al. 250). The second category includes genetic factors and determines the differences within populations belonging to the same ethnic group. Limited evidence exists that the differences within the microbiome of a single population vary from group to group, which can be interpreted as proof that there is still a possibility of genetic impact even after controlling for environmental factors (Dave et al. 249). Overall, while the exact weight of each factor is not known, it is certain that both environment and genetics play a role in microbiota formation to a certain extent.
Microbiome formation and development are closely associated with the functionality of the immune system. Non-pathogenic bacteria need to be tolerated by the immune system in order to survive and proliferate. For this reason, bacteria often mimic their native environment. For instance, gut bacteria are commonly coated in secreted immunoglobulin A due to its prevalence in gut mucosa (Donaldson et al. 10). Thus it is possible to suggest that differences in individual microbiomes are dictated, among other things, by a need to adapt to the specifics of the immune systems. However, it is also important to note that the impact is bi-directional, as the establishment of the microbiome also affects immune system performance. In the case of the gut microbiota, it has been suggested that its presence in an organism plays an important role in maintaining intestinal homeostasis by regulating the maturation of the system (Shi et al. 1). The mucosal immune system, which ensures the protection of the gastrointestinal tract, reacts to changes in microbiota composition in the form of abnormalities and inflammation, and, as a result, is able to respond more rapidly and accurately to the onset of disease.
As was mentioned in the previous section, microbiome composition differs among individuals. Several approaches have been used to establish the existence of these differences. First, deep sequencing techniques were used to determine the fecal microbiome variability observed within a single species. Since the results showed a high degree of variability (only 10% of the species remained unchanged during the course of the study), it has been suggested that the core composition was determined by unique individual characteristics (Dave et al. 250). Another method used to establish individual differences was the comparison of microbiota from twins who share the same genetic code. The results of the study demonstrated significant differences in composition, with less than 50% of the bacteria matching between the samples (Clemente et al. 1259). Thus it would be reasonable to assume that at least half of the bacteria in the microbiome are determined by environmental factors and, as a result, will be different for each individual. Finally, it should be pointed out that the composition of the remaining 50 percent is likely determined by specific host genomic loci (Clemente et al. 1259). In other words, it is reasonable to expect significant individual variability caused by a combination of genetic and environmental factors.
On the whole, an altered microbial composition could serve either as a cause or a consequence of disease. The main determinant responsible for this outcome lies in the properties of the bacteria that trigger an immune response (Li et al. 840). Most non-pathogenic bacteria responsible for gut community composition are coated in secreted immunoglobulin A, which greatly reduces the immune response. Importantly, some pathogenic organisms develop a similar coating, thus reducing the inflammatory processes and, by extension, delaying the onset of a disease. In addition, as was mentioned above, the introduction of factors that facilitate change in microbiota composition may lead to adverse health effects. The clearest example is the use of antibiotics, which is known to cause significant changes in the microbiome community. The resulting dysbiosis has been established to cause numerous diseases, such as inflammatory bowel disease, cancer, and obesity, among others (Clemente et al. 1263). These findings suggest that one microbe – one disease approach may be oversimplified and inaccurate.
Research on the microbiome is a relatively new direction in microbiology. Nevertheless, the available findings greatly improve our understanding of the microbiome’s influence on human health. Thus it is necessary to expand our knowledge about the microbiome in order to better understand the relationship between it and the state of human health.
Clemente, Jose C., et al. “The Impact of the Gut Microbiota on Human Health: An Integrative View.” Cell, vol. 148, no. 6, 2012, pp. 1258-1270.
Dave, Maneesh, et al. “The Human Gut Microbiome: Current Knowledge, Challenges, and Future Directions.” Translational Research, vol. 160, no. 4, 2012, pp. 246-257.
Donaldson, Gregory P., et al. “Gut Biogeography of the Bacterial Microbiota.” Nature Reviews Microbiology, vol. 14, no. 1, 2016, pp. 20-32.
Goodrich, Julia K., et al. “Human Genetics Shape the Gut Microbiome.” Cell, vol. 159, no. 4, 2014, pp. 789-799.
Li, Junhua, et al. “An Integrated Catalog of Reference Genes in the Human Gut Microbiome.” Nature Biotechnology, vol. 32, no. 8, 2014, pp. 834-841.
Shi, Na, et al. “Interaction between the Gut Microbiome and Mucosal Immune System.” Military Medical Research, vol. 4, no. 1, 2017, pp. 1-7.