And we humans provide the bacteria with a stable environment to live, along with a steady nutrient supply from the food we eat.
Think of your good bacteria as your own personal army- ready to protect you against invaders.
Interestingly, bacteria can actually “talk” to us through receptors found on the surface of our cells, called Toll-like receptors (TLR).
Our intestinal cells and immune cells express pattern recognition receptors called toll-like receptors (TLRs), that recognize bacterial products, including:
peptidoglycan (TLR2)- found on suface of Gram+ve bacteria
lipopolysaccharide (LPS) (TLR4) -found on surface of Gram-ve bacteria
flagellin (TLR5) -tail like structure that helps bacteria swim
bacterial DNA (TLR9)
Keep in mind that bacterial products can be recognized by our immune system even when the bacteria are dead or heat killed (i.e. pasteurization).
Most TLR signalling results in the activation of the transcription factor nuclear factor (NF)-κB, which in turn controls the expression of an array of inflammatory and immunoregulatory genes, including interleukin (IL)-1β, tumor necrosis factor (TNF)-a and IL-6, which elicit innate responses against invading bacteria and direct the development of adaptive immunity.
Imagine a Toll-like receptor as a type of “receiver”, similar to picking up a telephone. There are different Toll-like receptor “telephones” that can be used by different bacteria- as long as they have the correct identifier or “password,” which may include lipopolysaccharide (TLR4), a lipoprotein (TLR2) or even a tail (TLR5), or bacterial DNA (TLR9).
The conversations between bacteria and the cells in our intestine play a crucial role in keeping us healthy;
1) by directing inflammation,
2) controlling bacterial burdens and
3) maintaining the epithelial barrier- the single layer of cells which separates us from the outside world.
Studies show that changes to the normal “conversations” in our gut, may play a role in the pathogenesis of certain diseases, including inflammatory bowel disease.
Therefore, understanding how our body communicates with our resident bacteria is very important to understanding the underlying mechanism of health and disease- and perhaps may be the key to finding new treatments for disease.