Effect of Immunoglobulin G from Cows Immunized with Ferric Citrate Receptor (FecA) on Iron Uptake by Escherichia coli

摘要

The effects of immunoglobulin (Ig) G from cows immunized with the ferric citrate receptor (FecA) on iron uptake by Escherichia coli were investigated. Receptor FecA was purified from E. coli UT5600/pSV66. Cows were immunized with 400 μg purified FecA three times at 21 d intervals during late lactation and the nonlactat-ing period. Immunoglobulin G was purified by protein G affinity chromatography from colostral whey from cows immunized with FecA and from unimmunized control cows. The purified IgG from FecA immunized cows had higher IgG titers against FecA compared with control IgG. Fifteen E. coli isolated from intramammary infections and E. coli UT5600/pSV66were grown in an iron-depleted medium containing 1 mM citrate to induce FecA. The bacterial cells were mixed with 0, 2, and 4 mg/ml purified IgG, and ~(55)Fe was added to the assay. After 5, 10, and 15 min incubations at 37℃, samples were passed through 0.45-μm pore size filters. Filters were washed with saline three times, and the radioactivity of ~(55)Fe taken up by the bacterial cells on the filters was measured by a liquid scintillation counter. The measurements were expressed as numbers of ~(55)Fe atoms per colony-forming unit and transformed to Iog_(10). The assay was repeated three times for each isolate in a partially balanced incomplete block design. The presence of IgG decreased ~(55)Fe uptake by E. coli mastitis isolates and E. coli UT5600/pSV66. Anti-FecA IgG reduced ~(55)Fe uptake by E. coli greater than IgG from unimmunized cows.