Escherichia coli serogroups in breast-fed and bottle-fed infants.

1. Eighty-seven breast-fed and 95 bottle-fed infants were examined for differences in Escherichia coli serogroup pattern. 2) The serogroup composition was less complex in breast-fed infants. Fewer serogroups were found in the individual breast-fed child. However, with few exceptions, the same O groups were found in the two groups of infants. The prevalent O groups were among those also found most frequently in faeces from adults. 06 strains were more common in the breast-fed group, while 07 and 016 were not at all found in that group. 3) A special search for E. coli strains with Kl antigen showed that this antigen predominated in the bottle-fed infants. 4) Klebsiella and other Enterobacteriaceae were more frequently found among bottle-fed infants. 5) It is concluded that the intestinal milieu exerts a selective pressure which may result in a selection of different serotypes in two different intestinal milieus such as those examined.