Tapiainen T, Ylitalo S, Eerola E, Uhari M. Dynamics of gut colonization and source of intestinal flora in healthy newborn infants. APMIS 2006;114:812–7. The aim of the study was to evaluate the dynamics of gut colonization and the main source of intestinal bacterial flora in infancy in a quantitative manner using computerized analysis of bacterial cellular fatty acid (CFA) profiles. Each stool was collected from 10 healthy newborn infants during their first 2–7 days of life and a follow-up sample at 6 months of age. Stool samples were collected from mothers and nurses for comparison. Gas-liquid chromatography of the 159 stool samples was used to produce bacterial cellular fatty acid (CFA) profiles by means of a previously developed computerized program. The CFA profiles for the infants fluctuated from hour to hour during the first days of life and resembled those for both the mothers and the nurses, doing so all the more in the case of the five infants examined 6 months after birth. Gut colonization fluctuated markedly from hour to hour in the perinatal period. The effect of the maternal flora on the initial gut colonization may be less than expected as the fecal flora of infants started to resemble both the fecal flora of the mother as well as that of the first nurse.