Role of antibody and enterobactin in controlling growth of Escherichia coli in human milk and acquisition of lactoferrin- and transferrin-bound iron by Escherichia coli.

Growth of Escherichia coli NCTC 8623 in human milk was slow during the first 10 h of incubation, but this bacteriostatic effect had disappeared by 24 h. The bacteriostatic phase could be abolished by adding sufficient iron to saturate the lactoferrin in human milk, and also by adding supernatant from a 24-h milk culture or by adding enterobactin, an enterobacterial iron chelator. Growth in the presence of enterobactin was even more rapid than in the presence of excess iron. Partial loss of bacteriostatic activity could be achieved by absorbing the milk with bacterial antigens, but no clear correlation with removal of antibodies to O, K, or H antigens was apparent. When E. coli was grown in human serum trace-labeled with 59Fe, the organisms acquired iron from transferrin during growth. Cultivation of E. coli in a minimal medium supplemented with transferrin or lactoferrin doubly labeled with 125I and 59Fe showed that iron acquisition occurred without either assimilation or degradation of the iron-binding proteins.