Antibacterial Protein and Peptide Factors in Milk and Blood of Mammals: Interrelationships and Differences

Abstract

At present, antibiotics remain widely administered to prevent bacterial infections in livestock. Therefore, antibiotics and their metabolites inevitably contaminate target food products, specifically meat and milk. This trend promotes the development of bacterial resistance, either multidrug or pandrug, across all therapeutic classes. This review presents a systematic examination of endogenous antibacterial factors in mammals, comparing their profiles and combined action in blood and milk. Lysozyme and lysozyme-related proteins, transferrins, antibacterial cationic peptides, milk protein hydrolysis products, and other endogenous agents are considered. These classes of antibacterial factors share two structural features: a net positive charge and the presence of hydrophobic (primarily aromatic) functional groups. Although their mechanisms of action against bacteria vary, both the synthesis and activity of these factors are strictly regulated by the host immune system. These structural properties and biochemical hallmarks facilitate the development of therapeutic agents based not only on xenobiotics but also on endogenous mammalian metabolites. More in-depth study of the antibacterial activity of proteins and peptides in both mammalian milk and blood is required to develop viable alternatives to conventional antibiotics.