Probiotics in preterm infants: a controversial issue.

Current research is directed toward innovative dietary compositions that exert specific effects on health promotion and reducing the risk of diseases. For example, the demonstration that the gut microbiota is an important constituent in the intestine's mucosal barrier has led to new therapeutic strategies for infections as well as allergic and inflammatory conditions. Specific probiotic bacteria have been shown to stabilize the gut microbial environment and the intestine's permeability barrier, and to enhance systemic and mucosal IgA responses. These comprise important targets in the preterm infant, who is particularly susceptible to infection and inflammation and in whom the immature enterocyte responds to intraluminal antigens with proinflammatory cytokines. Recent data point to differences in immunomodulatory effects between candidate probiotic bacteria. Each probiotic strain is a unique component itself, and each strain has specific properties that cannot be extrapolated from other, even closely related, strains. Therefore, these properties of probiotic bacteria should be characterized during preclinical and clinical evaluations. Furthermore, because probiotics are a tool with which to modify the gut barrier and microbiota, the strains used must be obtained from acceptable sources with a proven safety record and efficacy to guarantee their future clinical applications. The approach of supplementation with single components, however, overlooks the role of dietary composition, with its range of nutrients and other potentially active components, and also the conceivable combined effects. Consequently, research now focuses both on characterizing specific probiotic strains and on how the food matrix and the dietary content interact with the most efficient probiotic strains.