Which of the following best describes the role of normal flora in the human body?

• A. Normal flora do not interact with the host immune system.
• B. Normal flora help prevent the colonization of pathogenic microbes by competing for nutrients and space.
• C. Normal flora are always harmful and cause disease in healthy individuals.
• D. Normal flora are only found in sterile body sites such as the bloodstream.

Answer: (B)

Verified step by step guidance

1. Understand the concept of normal flora: Normal flora, also known as microbiota, are the microorganisms that naturally reside on and within the human body without causing disease under normal conditions.
2. Recognize the interaction between normal flora and the host immune system: Normal flora often interact with the immune system, helping to train and modulate immune responses rather than being ignored.
3. Identify the protective role of normal flora: One of the key functions of normal flora is to prevent colonization by pathogenic microbes by competing for nutrients and physical space, effectively acting as a biological barrier.
4. Evaluate the incorrect options: Normal flora are not always harmful; they are generally beneficial or neutral in healthy individuals. Also, normal flora are typically found on non-sterile sites like skin, gut, and mucous membranes, not sterile sites such as the bloodstream.
5. Conclude that the best description of normal flora's role is their ability to help prevent pathogenic colonization through competition for resources and space.