It has been established that colonization of the gastrointestinal tract by Enterobacteriaceae and especially E. coli in newborn delivered by caesarean section occurs generally within the second day of life. On the 14th day, these bacteria inhabit the fecal flora of the majority of newborn. Hospital environment, as well as type of feeding do not seem to influence their frequency nor their level in the intestine of the infants born by caesarean section.