The question of the mechanism of action of probiotics and the manner in which breast milk reduces the incidence of NEC are important if we are to figure out for the future how to advance.
There are specific components of breast milk that can be considered to be part of an innate immune system in human milk, which protects the infant by inhibiting the binding of certain organisms and thus reducing infection. These oligosaccharides have been studied for a few years now, and as well as inhibiting the attachment of mucosal pathogens they promote the growth of probiotic organisms such as bifidobacteria even when added to artificial formulas. This has been shown in preterm infants also.
Lactoferrin is also a component of breast milk, largely absent in commercial formulae; lactoferrin is an important antibacterial agent in breast milk, and may have a role in the prevention of NEC.
A new publication seems to show that when breast milk is partially digested in vitro, the resulting mixtures are much less toxic to neutrophils than when the same procedure is performed using formula. The same was true of intestinal epithelial cells also, which may be more relevant to NEC.
Breast milk also promotes the growth of probiotic organisms and in fact breast milk often contains bifidobacteria, which are probiotics.
Another new publication suggests that probiotics may in part reduce NEC by effect on the expression of genes in the enterocytes that regulate inflammation. Other studies have shown that bifidobacteria when grown with prebiotic oligosaccharides affect intestinal epithelial function.
We still don’t have all the answers, but there is an accumulating evidence base which explains the actions of breast milk and of probiotics, which seem to overlap, and probably re-inforce each other.