Human microbiota

Human microbiota refers to the aggregate of microorganisms, including bacteria, viruses, fungi, and other microbes, that reside on and within human bodies. These microbial communities are found in various body sites such as the skin, mouth, gut, and respiratory tract, playing crucial roles in human health and disease. The study of human microbiota is a rapidly evolving field, shedding light on its contributions to metabolism, immune system function, and protection against pathogenic organisms.

Composition and Diversity

The human microbiota is incredibly diverse, with the gut microbiota being the most extensively studied. It comprises tens of trillions of microorganisms, including at least 1000 different species of known bacteria. The composition of the microbiota varies significantly from one individual to another, influenced by factors such as genetics, diet, age, and environment.

Gut Microbiota

The gut microbiota is predominantly made up of bacteria belonging to the phyla Firmicutes and Bacteroidetes. It plays a vital role in digesting dietary fibers, synthesizing essential vitamins (e.g., vitamin K and certain B vitamins), and regulating the immune system. Alterations in the gut microbiota composition have been linked to various diseases, including obesity, diabetes, inflammatory bowel disease (IBD), and colon cancer.

Skin Microbiota

The skin microbiota varies across different regions of the body, influenced by the local environment's moisture, temperature, and sebaceous gland density. It is essential for protecting the skin against pathogenic invasion, modulating the immune response, and contributing to the skin's barrier function.

Oral and Respiratory Microbiota

The oral microbiota is involved in the initial stages of food digestion and protects against pathogens. Imbalances in the oral microbiota can lead to conditions such as dental caries and periodontal disease. The respiratory tract microbiota plays a role in maintaining respiratory health and protecting against respiratory infections.

Functions

The human microbiota is involved in numerous physiological processes, including:

• Metabolic Functions: The microbiota assists in the breakdown of dietary components that are indigestible by the host, such as certain polysaccharides, producing short-chain fatty acids (SCFAs) that serve as an energy source for the host.
• Immune System Modulation: It plays a critical role in the development and function of the host's immune system, helping to distinguish between pathogenic and non-pathogenic organisms.
• Protection Against Pathogens: The microbiota can prevent the colonization of harmful pathogens by competing for nutrients and producing antimicrobial substances.

Dysbiosis and Disease

Dysbiosis, an imbalance in the microbiota, has been associated with numerous diseases. Factors such as antibiotics, diet, and stress can disrupt the microbiota, leading to conditions like antibiotic-associated diarrhea, allergies, and autoimmune diseases. Research is ongoing to understand the mechanisms by which dysbiosis contributes to disease and to develop microbiota-based therapies.

Research and Therapeutic Applications

Advancements in sequencing technologies and bioinformatics have significantly enhanced our understanding of the human microbiota. Probiotics and prebiotics are being investigated for their potential to modulate the microbiota and promote health. Fecal microbiota transplantation (FMT) has emerged as a treatment for recurrent Clostridioides difficile infection, showcasing the therapeutic potential of manipulating the microbiota.