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

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Abstract
Growth of E. coli NCTC 8623 in human milk was slow during the 1st 10 h of incubation, but this bacteriostatic effect disappeared by 24 h. The bacteriostatic phase was abolished by adding sufficient Fe to saturate the lactoferrin in human milk and by adding supernatant from a 24 h milk culture or by adding enterobactin, an enterobacterial Fe chelator. Growth in the presence of enterobactin was even more rapid than in the presence of excess Fe. Partial loss of bacteriostatic activity was achieved by absorbing the milk with bacterial antigens; 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 Fe 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 Fe acquisition occurred without assimilation or degradation of the Fe-binding proteins.