Inhibition of Mastitic Bacteria by Bovine Milk Apo-Lactoferrin Evaluated by In Vitro Microassay of Bacterial Growth

Abstract

An in vitro microassay was developed to evaluate antimicrobial properties of bovine apo-lactoferrin. The growth of coliform, staphylococcal and streptococcal bacterial strains in a defined synthetic medium was inhibited by bovine apolactoferrin (0.5-30.0 mg/ml). Addition of Fe-saturated lactoferrin to the synthetic medium did not inhibit growth of test strains. Inhibition by apo-lactoferrin was greater for coliform than gram-positive strains for all concentrations of apo-lactoferrin evaluated. No concentration of apo-lactoferrin was bactericidal for coliform or gram-positive strains. Inhibition of 2 coliform strains by apo-lactoferrin (10 mg/ml) was abolished by addition of Fe(III) to the assay system, indicating an Fe-dependent nature of apo-lactoferrin induced inhibition of bacteria. HCO3- supplementation of the growth system containing apo-lactoferrin (1 mg/ml) increased inhibition of 3 coliform strains by apo-lactoferrin. Addition of increasing concentrations of citrate (2.0 mg/ml) to an assay system containing apo-lactoferrin (5 mg/ml) resulted in a concomitant reduction of growth inhibition of 3 coliform strains. A potential relationship between the molar ratio of citrate to lactoferrin of the lacteal secretion and its capacity to inhibit coliform strains associated with mastitis was indicated.