What defines colonization?

• A. The presence and growth of microorganisms within a host without causing tissue invasion or damage
• B. The invasion of tissues by organisms causing tissue damage
• C. The onset of fever and systemic illness
• D. The complete absence of microorganisms in a host

Answer: (A)

Colonization is the presence and growth of microorganisms on or within a host without invading tissues or causing damage, and without producing symptoms. This includes normal flora that live on the skin, mucous membranes, or in the gut without causing disease. It differs from infection, where organisms invade tissues, cause damage, and may trigger fever or systemic illness. The other options describe tissue invasion with damage, systemic illness, or an absence of microorganisms, none of which define colonization.