| Foodborne illnesses are a significant problem and a major public health concern in the United States and throughout the world. The control of microbial pathogens in foods is a significant concern and numerous methods have been employed to control or prevent the growth of pathogenic microorganisms in food, including the use of synthetic and natural antimicrobial agents. There exist a plethora of literature on "natural" antimicrobial compounds (e.g. nisin, lactoferrin) and their possible use in food systems to eliminate or control the growth of pathogenic microorganisms. The actual antimicrobial mechanism of action for some antimicrobials has been extensively studied and well documented but for other potential natural biopreservatives, such as lactoferrin, the actual mechanism of action is not well defined. Lactoferrin is a 78 kilo Dalton cationic iron-binding antimicrobial glycoprotein produced in many mammalian secretions, including milk, tears, saliva, and serum. Previous research has focused on iron starvation and cell membrane damage. However, treatment with pepsin yields a peptide fragment, termed lactoferricin that lacks the iron binding sites and is still antimicrobial. It has also been hypothesized that the peptide, due to its small size, in comparison to the whole molecule, might be able to penetrate the outer membrane or that the smaller size of lactoferricin may facilitate its access to microbial cell surface components. The peptide and pepsin hydrolysate have been shown to depolarize the outer membrane of E. coli, however, this is likely not the mechanism of action. The data presented in this study demonstrate that the pepsin hydrolysate of lactoferrin (LfH) exerts its antimicrobial action on the inner membrane of E. coli O157:H7 by forming pores in the membrane. This membrane damage results in a loss of energy and ion balance (potassium ion (K+) efflux and decreases in intracellular ATP concentrations coupled with increases in extracellular ATP concentrations) leading to a collapse of membrane potential (DeltaPsi) and a loss of cell viability. |
