Effect of iron on serotypes and haemagglutination patterns of Escherichia coli in bottle-fed infants.

Strains of Escherichia coli isolated from faecal specimens of ten infants receiving breast milk, six receiving a cow-milk preparation with iron supplement (5 mg/l) and six the preparation without iron supplement (less than 0.5 mg/l), were serotyped and examined for their haemagglutinating activity. The Escherichia coli flora of breast-fed and bottle-fed infants consisted of one resident strain, accompanied by one or more transient strains. Changes in the serotype of the Escherichia coli flora and in the frequency of occurrence of strains associated with urinary tract infections were more often seen in bottle-fed than in breast-fed infants. In breast-fed and bottle-fed infants without iron supplement most strains of Escherichia coli were non-haemagglutinating, while most strains in infants bottle-fed with iron supplement showed mannose-resistant haemagglutination. It is concluded that human milk favours the establishment of a stable non-pathogenic Escherichia coli flora and that a low iron content in standard cow-milk preparation favours colonization with non-adherent strains of Escherichia coli.