In vitro growth inhibition of mastitis-causing coliform bacteria by bovine apo-lactoferrin and reversal of inhibition by citrate and high concentrations of apo-lactoferin

Publisher Website
Google Scholar
Abstract
Bovine apo-lactoferrin (apo-Lf) was added to in vitro cultures of 8 strains of coliform bacteria associated with bovine mastitis. As little as 0.02 mg of apo-Lf/ml resulted in marked inhibition of growth of all coliforms. Growth inhibition was lost if saturated Lf or Fe plus apo-Lf was added to the synthetic medium. The growth inhibition increased as the concentration of apo-Lf increased from 0.02 to 0.2 mg/ml for Klebsiella sp.(K1-21), K. pneumoniae (OARDC-A1) and Aerobacter aerogenes (55-12222) and 2 mg/ml for A. aerogenes (76-2414-1), Escherichia coli (60-Lilly), E. coli (66-S16) and Klebsiella sp. (K6-24). As the concentration of apo-Lf was increased above 0.2 or 2 mg/ml, there was less inhibition of growth except for E. coli (33-C4). Apo-Lf at 20 mg/ml was bactericidal for E. coli (33-C4). Results are compatible with the hypothesis that coliform bacteria resond to low-Fe environments by production of Fe-sequestering agents that compete effectively with apo-Lf for free Fe. Addition of apo-Lf plus citrate resulted in loss of growth inhibition. The molar ratio (citrate to apo-Lf) was more important than the absolute concentration of either component. A ratio of 75 resulted in 50% growth inhibition; ratios of .gtoreq. 300 resulted in < 10% growth inhibition. The ratio of citrate to Lf is important in evaluating Lf as a nonspecific protective factor of bovine mammary secretions.