ORIGIN OF THE NORMAL FLORA
The healthy fetus is sterile until the birth membranes rupture. During and after birth, the in-fant is exposed to the flora of the mother’s genital tract, to the skin and respiratory flora of those handling it, and to organisms in the environment. During the infant’s first few days of life, the flora reflects chance exposure to organisms that can colonize particular sites in the absence of competitors. Subsequently, as the infant is exposed to a broader range of organ-isms, those best adapted to colonize particular sites become predominant. Thereafter, the flora generally resembles that of other individuals in the same age group and cultural milieu.