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How do bacteria that normally live in the intestines limit the growth of invading bacteria?
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immune system
Stimulation of immune response by activated helper T cells. Activated by complex interaction with molecules on the surface of a macrophage or some other antigen-presenting cell, a helper T cell proliferates into two general subtypes, TH1 and TH2. These in turn stimulate the complex pathways of the cell-mediated immune response and the humoral immune response, respectively.
In the context of the immune system, the bacteria that naturally inhabit the intestinesâoften referred to as the gut microbiotaâlimit the growth of invading pathogens through a process known as colonization resistance.1
They employ several key strategies to protect the host:
- Competition for Resources: Beneficial gut bacteria compete directly with harmful microbes for essential nutrients and physical attachment sites on the intestinal lining, effectively crowding out invaders.1
- Production of Inhibitory Substances: These commensal organisms secrete a variety of proteins and other chemical compounds that specifically inhibit the growth of invading bacterial species, thereby enhancing their own survival and the host's defense.12
- Environmental Modification: By maintaining a balanced microbial community, these bacteria help reinforce the intestinal barrier and regulate inflammatory responses, making the environment less hospitable to pathogens.1
When this normal bacterial population is disruptedâfor example, by the use of antibioticsâthe loss of this competitive pressure can allow dangerous bacteria to multiply, flourish, and potentially invade the body's tissues.31