Final answer:
The first line of defense in the microbiota is characterized by physical barriers that prevent pathogens from entering the body and establishing themselves in the soft tissues. These physical barriers include the skin, mucous membranes, and endothelia throughout the body.
Step-by-step explanation:
The first line of defense in the microbiota is characterized by physical barriers that prevent pathogens from entering the body and establishing themselves in the soft tissues. These physical barriers include the skin, mucous membranes, and endothelia throughout the body, which serve as a protective barrier against microbes. Tight cell junctions in these tissues prevent microbes from passing through. Additionally, the resident microbiota compete with pathogens by occupying available cellular binding sites and competing for nutrients.