Introduction
A microbiome refers to all the genomes present within the microorganisms within a specific environment. A microbiota refers to a community of microorganisms. Within the human gastrointestinal tract, there are so many microorganisms (approximately 100 trillion) to the point that some scientists virtually consider it as an organ of the human body.
In terms of function, the gut microbiota has several. For example, they are heavily relied upon for the fermentation of non-digestible substrates such as intestinal mucus or dietary fibres. Also, this fermentation then facilitates an environment that is favourable to the production of specialized microbes which can produce gases and short-chain fatty acids (SCFAs). These acids play a vital role in modulating host metabolic health and in maintaining gut integrity through means such as regulating luminal pH and mucus production. That being said, many factors influence the health of someone's gut microbiota. This review will discuss the main factors that do so, based on analysing existing scientific research within the field.
Diet A review of existing scientific literature shows that an individual's diet can significantly impact the gut microbiome, leading to massive changes in human health. For example, high-fat diets have been shown to reduce the bacterial populations of A. muciniphila and Lactobacillus, which are both associated with healthy metabolic levels.
Furthermore, the word probiotics - foods or supplements formed through bacterial fermentation - is frequently brought up when discussing healthy intestinal flora. Probiotics (literally meaning "for life") inhibit the growth of pathogenic bacteria that would otherwise change the level of homeostasis within the gut microbiota. This occurs due to their nature to stimulate epithelial barrier function, competitively removing pathogens from their traditional binding sites, secreting anti-microbial components, and limiting these pathogen's access to vital nutrients. As a result, probiotics are often considered a vital part of anyone's diet to help maintain a healthy gut microbiota.
Exercise
Newer studies highlight how exercise has the potential to increase levels of beneficial microbial species, improve microflora diversity, and can also foster the development of commensal bacteria. Exercise is also known to improve the Bacteroidetes-Firmicutes ratio within the body. This is a ratio of two dominant phyla of bacteria present in the gut microbiota, with higher ratios found within obese people. Lowering this ratio (which can be facilitated by exercise) thus has the potential to reduce obesity-related pathogens, weight, and gastrointestinal disorders. While these findings are backed by data, it must be known that additional research expanding upon the mechanism for how this works is still needed within the scientific community.
Environment and Pollution An abundant amount of environmental chemicals has displayed abilities to inhibit gut microbiota bacterial growth or shown abilities to cause dysbiosis (an imbalance of microbial species) in vivo and in vitro. This is significant as previous studies have linked dysbiosis to a large amount of intestinal and systemic disease.
A lot of said disorders are also readily linked to exposure to environmental chemicals. Other studies highlight how exposure to environmental chemicals may lead to dysregulated immune responses. Some studies point to this as possibly due to how exposure to such chemicals may impact the standard colonization of one's gut by such bacteria, leading to greater effects on a person's physiology in later life. Experiments involving mice further highlight this, as mice that drank water that was environmentally polluted with water had lower levels of microbial species overall. Additionally, heavy metal-consuming mice had lower levels of Lachnospiraceae. This is significant as lower levels of Lachnospiraceae have been associated with intestinal inflammation and suggested to increase the likelihood of developing colitis.
Antibiotic usage
The human microbiome is almost always exposed to a large amount of antibiotics, either directly through medically administered drugs or indirectly through the consumption of crops and farm animals that had been treated with such drugs while alive. Antibiotics, then, play a significant part in altering the diaspora of microorganisms within the gut flora. Studies show that they can disrupt community structure enough to lead to massive alterations in available resources alongside organism-to-organism interactions. Additionally, more novel research in mice shows that antibiotics lead to an increase in the levels of host-produced free sialic acid in the gut. This is harmful, as these acids have the potential to be utilized by opportunistic pathogens such as Clostridium difficile and Salmonella typhimurium to further facilitate their growth.
On a general level, most studies analysing the impact of antibiotics on gut flora taxonomic composition find lower levels of bacterial diversity, declines, and expansions in the abundance of specific taxa, generally long-lasting effects in most environments, alongside host-specific impacts. In particular, wide-ranging and multi-purpose antibiotics utilised against anaerobes, such as clindamycin, tend to have the most damaging and lengthy effects on gut flora constitution
Conclusion and Future Directions From this review, it is evident that gut microbiota homeostasis is crucial in maintaining an individual's health. It is also clear that the formation of this microbiota in terms either of its composition or relative abundance of specific microorganisms is influenced by several different factors. Additionally, disorders or imbalances within this gut microbiota are associated with several diseases, and maintaining optimal levels of these organisms is crucial to help in the prevention or treatment of them. In light of this. several treatment opportunities such as utilising prebiotics, probiotics, or even faecal microbial transplants (which is a medical procedure wherein a small sample of faeces is transplanted from an individual with a healthy colon to one with a diseased colon) act as promising options for both the prevention and treatment of disease. That being said, there still needs to be a greater level of research into how manipulating such gut microbiota can lead to improved health outcomes. Moreover, studies that focus on detecting the missing functions of the gut microbiota during situations of disease will aid in the identification of relevant treatments (such as faecal microbial transplants or probiotic intake) that would be capable of attaining the desired outcome.
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