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Antibacterial factors in cows’ milk and colostrum : immunoglobulins and lactoferrin Facon, Michel Jean


The objectives of this study were: 1) to test the antibacterial activity of a pepsin digest of bovine lactoferrin, containing the peptide lactoferricin, in complex media; 2) to detect specific antibodies to human enterotoxigenic Escherichia colt in bovine milk or colostrum; and 3) to investigate the potential of a cell culture system to study and estimate the biological activity of milk immunoglobulins. The pepsin digest of lactoferrin was bactericidal against Salmonella enteritidis in 1% peptone, but no substantial antibacterial activity could be demonstrated in trypticase soy broth or in some selected foods. Calcium at a concentration of 5 m?s’I was sufficient to inhibit the antibacterial activity of the digest. Addition of lysozyme or EDTA enhanced the antibacterial activity of the digest, but not sufficiently to overcome the effect of inhibitors in the foods of interest. The activity of the digest was also inhibited by bile salts. These findings raise doubts about the potential for addition of lactoferricin to foods. Antibodies to the colonization factor antigen CFA 1 of enterotoxigenic E. colt were detected in bovine colostrum by hemagglutination inhibition. Concentrations of antibodies to CFA 1, estimated by ELISA, ranged from 0.55 to 5.2 .tg/ml in colostrum samples of nonvaccinated cows. Samples of milk immune concentrates from vaccinated and non-vaccinated cows were also tested. Vaccination increased the concentration of specific antibodies relative to the total IgG content of the samples tested. Invasion of HeLa cells by Salmonella enteritidis, S. typhimurium and enteropathogenic E. coli was inhibited by addition of bovine colostrum to cell culture medium. Inhibition levels ranged from 73% to over 99%. The immunoglobulin-containing fraction, isolated from colostrum by affinity chromatography on a protein G-agarose column, inhibited invasion by S. typhimurium. An unidentified high molecular weight factor in the non-immunoglobulin fraction also inhibited invasion of HeLa cells. No inhibitory activity was found in low molecular weight fractions. The results suggest that bovine colostrum contains both immunoglobulin and non-immunoglobulin inbibitors of invasion of HeLa cells by the bacteria tested. HeLa cell cultures have the potential to be a convenient method for the study and evaluation of antibacterial properties of bovine milk.

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