[Kinetics of establishment of digestive microflora in the human newborn infant as a function of the kind of milk]

Abstract

The digestive tract of human infants, sterile at birth, is colonized by some bacterial genera within less than 48 h. Among the factors involved in the implantation of a given bacterial genus, the type of milk fed plays a major role. We studied the development of fecal flora in 1 to 8-day old babies, either breast-fed or bottle-fed with humanized milk. In breast-fed infants the microflora reached an equilibrium towards the age of 5 days and then hardly varied until the change of feeding. Escherichia coli and Streptococcus were established first and Bifidobacterium later. At the age of 5 days, the strictly anaerobic flora was exclusively composed of Bifidobacterium in 85% of cases. The development of other strictly anaerobic bacteria was repressed, particularly that of Bacteroides. In infants receiving humanized milk, Escherichia coli (or sometimes other enterobacteria) also appeared very early in the digestive tract. However, the strictly anaerobic flora was either absent (40% of cases) or composed of one or more genera (e.g. Bacteroides, Bifidobacterium, Plectridium). These findings in human infants show that it is mainly the establishment of the strictly anaerobic flora which is affected by the type of milk fed.