Answer :
Option C, An opportunistic pathogen may also be a commensal bacteria.
Commensal bacteria influence the immune system of the host to trigger defense mechanisms that thwart pathogen invasion and colonization. On the other hand, by creating antimicrobial compounds and signals and competing with other bacteria for nutrients & adhesion sites, these bacteria could directly restrict the growth the respiratory infections.
In addition to providing the host with vital nutrients, commensal bacteria also protect it from opportunistic diseases. They contribute to the mechanisms that modulate the immune system and the development of gut architecture. The host, in contrast, hand gives the bacteria nourishment and a consistent habitat.
But on occasion, particularly when they spread outside of their natural habitat, these commensal microorganisms might cause illness.
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