Effects of bovine antibodies directed against ferric citrate receptor of Escherichia coli, FecA, on bacterial iron acquisition, bacterial growth, and severity of experimentally induced bovine mastitis

Effects of antibodies directed against ferric citrate receptor, FecA, of Escherichia coli on bacterial iron acquisition, growth, and E. coli mastitis were investigated.; Twenty-one cows were assigned to one of three treatments: (1) FecA immunization, (2) Escherichia coli J5 immunization, and (3) unimmunized controls. Immunizations were: (1) subcutaneous injection at 14 d prior to drying off, (2) intramammary infusion at 7 d after drying off, and (3) subcutaneous injection at 28 d after drying off. Intramammary challenge was by infusion of approximately 60 colony-forming units of E. coli 727 into one uninfected mammary gland approximately 3 weeks post parturition. FecA was immunogenic in cows. The increased antibody titers against FecA were associated with decreased peak bacterial counts in milk from challenged mammary quarters. FecA immunized cows tended to have lower rectal temperature and bacterial counts in milk following the bacterial challenge.; Immunoglobulin (Ig) G was purified from colostral whey for each treatment group. Fifteen field isolates of E. coli and E. coli UT5600/pSV66 were grown under iron-deplete conditions with citrate to induce FecA. Escherichia coli were incubated with IgG and 55Fe at 37°C. After 5, 10, and 15 min of incubation, the radioactivity of E. coli that transported 55Fe was measured by liquid scintillation counting. The presence of anti-FecA IgG reduced 55Fe uptake by E. coli compared with control IgG.; Fourteen field isolates of E. coli and E. coli UT5600/pSV66 were cultured in the presence of anti-FecA IgG, anti-J5 IgG or control IgG under iron-deplete conditions with citrate at 37°C. Bacterial numbers were determined after 0, 6, 12, and 24 h incubation. To investigate effects of exogenous iron, 50 μM FeCl₃ were added to the assay. The presence of IgG decreased growth of E. coli over iron-depletion alone, however growth did not differ among IgG sources. Exogenous iron increased growth in the presence of anti-FecA and anti-J5 IgG, but not control IgG.; Anti-FecA IgG decreased iron uptake and growth of E. coli in vitro, however the immunization with FecA had minimal effects on severity of clinical E. coli mastitis in cows.