Bacteriostatic effect of human milk and bovine colostrum on Escherichia coli: importance of bicarbonate

Abstract

At pH 7.4 and in the presence of NaHCO3, human milk and bovine colostrum inhibited the growth ofEscherichia coli 0111. Adding sufficient iron to saturate the iron-binding capacity of the lactoferrin present in the milk or colostrum prevented bacteriostasis. At pH 6.8 neither milk nor colostrum inhibited E. coli 0111. Adjusting the pH to 7.4 with NaHCO3 resulted in the development of bacteriostatic activity. Adjusting the pH to 7.4 with NaOH was ineffective. Dialyzed colostrum and milk inhibited bacterial growth at pH 6.8 in the absence of added NaHCO3; addition of citrate or iron abolished bacteriostasis. The chromatographic elution profile of tyrosyl-transfer ribonucleic acid (tRNA) from iron-replete E. coli differs significantly from that of tyrosyl-tRNA from irondeficient organisms. Examination of the elution profile of tyrosyl-tRNA from E. coli 0111 growing in colostrum without added NaHCO3 showed that such bacteria were fully replete in iron. The nature of the elution profile of tyrosyl-tRNA also showed that iron was freely available to the bacteria when citrate was added to dialyzed colostum but not available in its absence, even at pH 6.8. Results support the idea that the bacteriostatic action of milk and colostrum, due to the combined action of antibody and lactoferrin, depends on the addition of bicarbonate to counteract the iron-mobilizing effect of the citrate normally present in these secretions.

Effects of Powdered Human Milk Fortifiers on the Antibacterial Actions of Human Milk

“…The addition of medium-chain monoglycerides to human milk has been reported to inactivate Haemophilus influenza and Group B Streptococcus (GBS) 2 and iron may affect the milk's lactoferrin activity. 3 However, the effects of these new fortifiers on the anti-infective properties of human milk have not been reported. Therefore, the present study was designed to evaluate the effects of the addition of these powdered fortifiers, iron, and MCT on the anti-infective properties in human milk.…”

Lactoferrin and Citrate Concentrations at Drying‐off and During Early Mammary Involution of Dairy Cows

“…In the mammary gland, efficacy of Lf is negatively correlated with citrate content of the milk (Bishop et al, 1976). Bicarbonate, which is required for the binding of iron by Lf, can overcome the effect of citrate especially during the dry-cow period, when citrate is absorbed from the udder to blood while bicarbonate diffuses from blood to the udder (Reiter et al, 1975;Griffith and Humphrey, 1977). The concentration of Lf varies from 0.02 to 0.35 mg ml )1 in the milk of lactating healthy cows (Welty et al, 1976).…”

Specific binding of lactoferrin to Escherichia coli isolated from human intestinal infections

“…This protein is suggested as an important non-specific defence factor and its level rises significantly during inflammation or endotoxic shock (15,63). Lf has been shown to inhibit the growth of E. coli and certain other microorganisms in vitro (6,20,47,57). The antimicrobial property is mainly attributed to the iron-chelating capacity of Lf, leading to iron deprivation of bacteria (20,34).…”

“…Lf has been shown to inhibit the growth of E. coli and certain other microorganisms in vitro (6,20,47,57). The antimicrobial property is mainly attributed to the iron-chelating capacity of Lf, leading to iron deprivation of bacteria (20,34). However, some pathogens may overcome Lf-mediated iron deficiency by producing siderophores (7,38).…”