Chapter 5 / Role of milk carbohydrates in preventing bacterial adhesion

Abstract

[ENG]This chapter examines the complex biological role of milk carbohydrates, particularly human milk oligosaccharides (HMOs), as a primary defense mechanism against neonatal infections. While lactose serves as a major energy source, the focus here is on the diverse array of glycoconjugates—including free oligosaccharides, glycoproteins, and glycolipids—that function as potent anti-adhesive agents.Molecular Mimicry and Anti-Adhesion MechanismThe fundamental premise is the inhibition of bacterial adherence to host tissues, which is the requisite first step for most infectious diseases. Many pathogenic microorganisms, such as various strains of Escherichia coli (ETEC, EPEC, EHEC), Campylobacter jejuni, and Vibrio cholerae, utilize surface lectins or adhesins to recognize and bind to specific carbohydrate sequences on the surface of the infant's intestinal epithelium.Milk carbohydrates act as "soluble decoy receptors." Because their chemical structures mimic the carbohydrate moieties found on the host’s cell membranes, they compete with the host receptors for bacterial binding sites. Once the pathogens or their toxins bind to these soluble milk glycans instead of the intestinal wall, they are neutralized and eventually flushed out of the gastrointestinal tract, preventing colonization and subsequent infection.Compositional Complexity and Genetic VariabilityHuman milk is uniquely rich in complex oligosaccharides (12–14 g/L) compared to bovine milk, which contains significantly lower concentrations and simpler structures. The structural diversity of HMOs is largely determined by the mother's genetic profile, specifically the Secretor (Se) and Lewis (Le) blood group systems. These genes encode specific fucosyltransferases that determine the presence of terminal epitopes like $\alpha$1-2 linked fucose. For instance, "Secretor" mothers produce milk rich in 2'-fucosyllactose, which is highly effective against specific enteric pathogens.Analytical MethodologiesThe chapter also details the rigorous technical processes required to study these molecules. Due to their low concentration and structural microheterogeneity, isolation involves sophisticated techniques such as ultrafiltration and gel filtration chromatography. Characterization is achieved through High-Performance Liquid Chromatography (HPLC), High-Performance Anion-Exchange Chromatography (HPAEC), and Mass Spectrometry (notably MALDI-TOF), which allow for the identification of specific glycan sequences and linkage patterns.ConclusionThe protective effect of milk carbohydrates provides a crucial advantage for breastfed infants, significantly reducing the morbidity associated with diarrheal diseases. The chapter concludes that while modern infant formulas attempt to replicate this protection, the immense structural complexity and biological specificity of human milk carbohydrates remain a major challenge for food engineering and clinical nutrition.