Which body site is normally colonized by normal microbiota?

• A. Lungs
• B. Trachea
• C. Cervix
• D. Skin

Answer: (D)

Normal microbiota inhabit surfaces that are exposed to the environment, providing a protective barrier by occupying niches and producing substances that inhibit potential pathogens. The skin is a prime example: its large surface area, hair follicles, and sebaceous glands create many microhabitats where residents like Staphylococcus epidermidis and Cutibacterium species persist throughout life. This persistent colonization is a normal, healthy state and helps defend against invasion by sending out competitive signals and acids that deter others.

In contrast, the lower respiratory tract—lungs and trachea—is normally sterile because mucociliary clearance, antimicrobial factors, and immune defenses continually remove microbes and prevent establishment. The cervix can host microbial communities, but the question emphasizes a site classically described as normally colonized by normal flora in healthy individuals, which the skin clearly is.