Which body site is not normally colonized by large numbers of normal flora?

Which body site is not normally colonized by large numbers of normal flora?

• A. Lungs
• B. Colon
• C. Skin
• D. Vagina

Answer: (A)

Normal flora are abundant on surfaces that provide nutrients and moisture, such as the colon, skin, and vagina. The lungs, however, are kept relatively sterile in healthy individuals by mucociliary clearance, coughing, and immune defenses, so they do not harbor large, resident microbial populations. Therefore, the lungs are not normally colonized by large numbers of normal flora. If a lung sample shows many bacteria, it may reflect contamination from the upper airway or indicate an infection rather than normal flora. The colon, skin, and vagina are classic sites for dense resident microbiota because their environments support stable, long-term colonization.

Normal flora are abundant on surfaces that provide nutrients and moisture, such as the colon, skin, and vagina. The lungs, however, are kept relatively sterile in healthy individuals by mucociliary clearance, coughing, and immune defenses, so they do not harbor large, resident microbial populations. Therefore, the lungs are not normally colonized by large numbers of normal flora. If a lung sample shows many bacteria, it may reflect contamination from the upper airway or indicate an infection rather than normal flora. The colon, skin, and vagina are classic sites for dense resident microbiota because their environments support stable, long-term colonization.