The trick is to keep the patient’s gut flora healthy -- healthy as a breastfed baby’s. The typical medical approach is to kill off lurking pathogens with a dose of antibiotics. The problem with this approach is that it is both indiscriminant and selective, i.e. it kills both pathogens and beneficial bacteria, but it also provides a selective advantage for the antibiotic resistant hospital strains of opportunistic pathogens.
Humor break: Why do babies spit up half-digested breastmilk and then smile? Answer: Pepsin produces antimicrobial peptides from milk proteins. The baby smugly acknowledges that she knows that she has just protected her upper respiratory and digestive tracts against bacterial pathogens.
Pepsin hydrolyzes proteins next to aromatic amino acids and away from the basic amino acids, arginine and lysine. That means that heparin-binding domains, which consist of groups of basic amino acids in a hydrophobic environment, are clipped out intact from proteins by pepsin. Thus, babies sucking down milk make their own isolated peptides with heparin-binding domains.
Many organisms, from fruit flies to frogs to humans, produce anti-microbial peptides. They also produce proteins with nucleic acid-binding domains and nuclear localization signals and heparin-binding domains and IP3-binding domains. If all of those binding domains are clipped out by pepsin and the peptides are compared to the anti-microbial defensive peptides, amazingly they are all the same. All have groups of basic amino acids among hydrophobic neighbors, and all are toxic to bacteria.
Lactoferrin is a major component of milk whey. It binds iron and heparin. It can be digested by pepsin into an an anti-microbial peptide, lactoferricin. Baby’s smile and spit-up on your shoes when you say lactoferrin.
Transgenic mice that produce porcine lactoferrin in their milk, transfer extra lactoferrin their little suckling mouse pups and that extra lactoferrin gives extra protection against bacterial and yeast pathogens. That is the experimental justification to suggest that treating patients at risk of nosocomial infections (I guess that would mean every patient in contact with a nurse or doctor) with oral lactoferrin should selectively eliminate the pathogens. Lactoferrin is prebiotic and supports the growth of probiotic gut flora.
Yen CC, Lin CY, Chong KY, Tsai TC, Shen CJ, Lin MF, Su CY, Chen HL, Chen CM. Lactoferrin as a natural regimen for selective decontamination of the digestive tract: recombinant porcine lactoferrin expressed in the milk of transgenic mice protects neonates from pathogenic challenge in the gastrointestinal tract .J Infect Dis. 2009 Feb 15;199(4):590-8.