However, the best strategy has yet to be developed as it does not appear that pasteurizing maternal milk changes the overall incidence

of late onset GBS disease in preterm infants [38]. In a recent review article of cases of late onset GBS disease from breast milk, GBS was found in 0–2% of raw milk samples and 1.4% of pasteurized milk samples [9]. Two main mechanisms of acquisition have been proposed: following colonization of the neonatal oropharynx at the time of birth, mothers may develop colonization of the milk ducts through ascending infection from the neonate, due to the retrograde flow of milk associated with suckling. The infant is then reinfected as the concentration of bacteria increases in the breast milk [39]. This may occur with or without mastitis depending LY2157299 in vitro on additional factors such as milk stasis

and bacterial load [40]. In most of the case reports of GBS disease associated with breast milk there is no sign of maternal mastitis, indicating silent maternal duct colonization [9]. However, recent studies in animal models and discovery of lactobacilli in breast milk after oral administration suggest that bacteria from the maternal digestive tract may also colonize the breast. [41] It has also been suggested that lactic acid bacteria may transfer from the mother’s gut to breast milk and through the milk to the infant’s digestive tract [42]. The epidemiological relationship between neonatal BYL719 in vivo and maternal derived GBS isolates in breast milk has been confirmed by polymerase chain reaction (PCR) [43]. However, it is not clear whether the LO disease relates to infected breast milk or is a result of gut translocation from an already colonized infant. GBS may infect the submucosa of the gastrointestinal tract either through

a defect in the epithelial cell layer, or by concomitant infectious agents [33]. As neonatal gastric acid secretion is reduced, more bacteria may reach the intestinal mucosa. This is supported by findings that preterm infants fed with contaminated maternal milk via nasogastric tube have developed nearly GBS disease [44]. Breast milk is the main source of non-pathogenic bacteria to the infant gastrointestinal tract. Intestinal bacteria are one of the most important stimuli for the development of mucosa-associated lymphoid tissue (MALT) in the neonatal small intestine [45] and produce organic acids that prevent growth of enteric pathogens. Additionally, breast milk and colostrum contain many components with antimicrobial and immunomodulatory properties that are believed to impair translocation of infectious pathogens [46]. Some of these substances compensate directly for deficiencies in the neonatal immune system and enhance survival of defense agents, including secretory IgA (SIgA), lactoferrin, lysozyme, IFN-γ; some adapt the gastrointestinal tract to extrauterine life, i.e.