The objective of this study is to show how the gut microbiome influences human health positively and negatively.
Gut Microbiomes are collective genomes of microbiota present in the gut of the human body. The gut starts from the mouth, extending through well defined anatomical regions - the esophagus, stomach, small intestine, colon, rectum - and ending at the anus.
The properties of the human microbiome and the host-microbiota interactions have been largely unknown for years. However, advances in sequencing technologies and different microbiome projects such as Human Microbiome Project have broadened the information about the roles of the human gut microbiome in human health.
Development of Human Gut Microbiome: From Fertilization to Birth
Some bacterial cells of the uterine cervix may enter with the sperm and reach the egg at the same time of fertilization. Uterus, placenta, and blood often appear to be void of microbiota but they may contain bacterial DNA. Also, the maternal microbiota may exert an indirect effect on the fetus through maternal factors that cross the placenta. Extensive colonization of the infant microbiome occurs at the time of birth. The method of delivery also has a role to play in the microbiome composition of the infant. Infants born through natural birth are exposed to a greater diversity of microbiota, compared to those born through Caesarian section. The sterile operating room and delayed contact with the mother create favorable conditions for hospital flora to colonize the newborn's system.
Development of gut microbiome - After Birth
Here, we will discuss the factors that affect gut microbiome development after birth.
They include:
- Type of feeding
- Antibiotic usage
- Birth environment
- The physiology of the colonization site, etc.
Milk is the first food that is introduced into the gut postpartum and the composition of the milk is believed to directly impact shaping the early gut microbiota. Formula-fed infants tend to have diverse gut microbial communities that contain higher levels of Facultative and strict anaerobes. Fecal samples from breastfed infants are less complex and contain a higher number of aerobic organisms. However, research has proven that once weaning starts and solid food is introduced, the differences in microbial population between breast and formula-fed infants are lost. But it is worthy to be noted that microbial colonization before weaning influences the health of the infant.
Roles of Human Gut Microbiome in the body
They include:
1)Metabolic functions
2) Immunity
3) Colonization Resistance
4) Human development
5) Nutrition
1) Metabolic functions - Gut microbiota are integral to human digestion and nutrition and they can generate nutrients from substrates that are otherwise indigestible by the host. For example, xyloglucans are commonly found in dietary vegetables such as lettuce and onions, and the capacity for microbial digestion of xyloglucans was recently mapped to a single locus in a certain species of Bacteroides. The ability to digest Xyloglucans is a relatively rare trait in members of the phylum Bacteroides and it has been proven that at least one of these rare Bacteroides species are present in most individuals. These findings illustrate how humans have cultivated mutually beneficial relationships with gut microbiota with implications for diet and nutrition. Microbes liberate Short Chain Fatty Acids (SCFA) and SCFAs are important energy sources for intestinal mucosa and critical for modulating immune responses.
2) Immunity
A healthy interaction between our immune system and gut microbiota is crucial for the maintenance of our body's homeostasis and health. Some microbes are known for promoting the differentiation of anti-inflammatory regulatory T cells (Treg) and this influences immune homeostasis. Some non-pathogenic species of Clostridia from different clusters play roles that control Treg development. Also, these microbiota-derived SCFAs have been shown to confer protection to the gastrointestinal barrier integrity against the disruptive effects of proinflammatory cytokines.
3) Colonization Resistance
Another important role of human microbiota is colonization resistance where indigenous microbiota confers protection to host against colonization of pathogenic invader and prevention against overgrowth of pathogenic microbiota. The mechanisms can be classified into two -
1)Direct interaction between human microbiota and pathogens in competing for shared niches and nutrients, hence suppressing the growth and colonization of pathogens.
2) Enhancement of host defense machinery by human microbiota to suppress pathogen.
Gut Microbiome and Associated diseases
External factors (such as antibiotic consumption, a dietary component, psychological and physical stress) and host factors can induce dysbiosis in the gut microbiome. Dysbiosis impairs the normal functioning of gut microbiota in maintaining host wellness and this can lead to the dysregulated production of microbial-derived products/metabolites which might be harmful to the host, causing a wide range of diseases, for example, Inflammatory Bowel Diseases.
Inflammatory Bowel Diseases (IBD)
This is a microbiome-associated disease. IBD is a group of multifactorial, persistent, and recurring gastrointestinal inflammation. It is associated with relapsing fever, diarrhea, and abnormal pain. Research has shown that the inappropriate host immune response against gastrointestinal microbiota in genetically predisposed individuals is associated with severe inflammation.
Celiac Disease:
Dysbiosis (imbalance of gut microbiota) has been proven to be associated with risk factors if autoimmune diseases such as celiac disease. Celiac disease is a multifactorial chronic immune-mediated disorder in the small intestine. It is characterized by permanent intolerance to dietary gluten and prolamines in some individuals. Gut dysbiosis (imbalance of gut microbiota has been reported in Celiac disease patients, in which the active phase of Celiac disease is characterized by a remarkable decrease in gram-positive bacteria. Hence, we can deduce that Gut dysbiosis plays a role in the pathogenesis of the Celiac disease.
It has also been proven that Gut dysbiosis plays a role in obesity, cardiovascular diseases, type 11 diabetes, liver abnormalities, and so on. However, for dysbiosis to occur and play a role in these diseases, there must have been a factor behind it.
Factors that cause dysbiosis include:-
1) Age
2) Stress
3) Dietary Change (High fat, high sugar diet)
4) Excessive intake of alcohol
5) Poor hygiene
6) New medications such as antibiotics.
Hence, Gut microbiomes influence our health in diverse ways, depending on various conditions.
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