Colonization of the gastrointestinal tract.

The alimentary tract is sterile at birth but colonic colonization is relatively complete by the end of the first week of life. The upper alimentary tract is colonized by microorganisms normally inhabiting the oral cavity. The colon on the other hand appears to be colonized by microorganisms originating in the maternallower alimentary tract. The colonic flora of infants is affected by diet (breast or formula feedings). The presence of a "fecal-type" flora in the proximal small bowel should be considered abnormal. Most authors agree on the need to define the role of the microflora in health and disease.