Bacteriophages and human microbiome

There is also a more detailed classification, for example, bacteria behind the ear may be different from the bacteria on the back of the hands (communities at these two places may be compositionally different), and bacterial communities throughout the gastrointestinal tract may be differentiated as well. The microbiome composition and function affects its host, enhances food metabolism, creates a barrier for defense against dangerous pathogens and provides it with essential metabolites and vitamins. In addition, the human microbiome composition and function may be associated with various diseases and disorders, including irritable bowel syndrome, gingivitis, atopic dermatitis, outbreaks of bacterial vaginosis, oral cancer, colon cancer and nonalcoholic fatty liver disease.

Our healthy microbiome includes a virome that is mainly composed of phages.

Lytic phages and prophages play a key role in regulating bacterial balance, including healthy human microbiome. It can be assumed that our regular consumption of phages from natural foods and water resources is essential for the sustainment of the healthy microbiome. This explains why allergies to pure phage preparations do not develop in humans, and why the innate immune system does not respond significantly to bacteriophages, it would disrupt the microbiome balance. In humans, phages are partially or mostly degraded by the reticular endothelial system. But they may survive for quite a long time, multiplying in host bacteria and staying in balance with them.

Studies with animals, humans and tissue cultures have shown that phages are also associated with the mucosal surfaces. It helps them enhance their efficacy and at the same time cause a beneficial immune response: mucous membrane is the main entry point for bacterial infections, and it has been shown that phages are significantly abundant in mucus due to the interaction of mucin glycans and Ig-like protein domains on some phage capsids. Metagenomic analysis has shown that these Ig-like phage proteins are very common in the vicinity of mucous membranes. This led to the model that supports the idea of co-evolution of bacteriophages and host bacteria.