Breast milk protects the neonate from bacterial translocation

Abstract

Clinical and experimental evidence suggests that breast milk enhances the neonatal gut barrier. Using bacterial translocation (BT) as a measure of gut barrier function, a series of experiments was designed to explore the relationship between the neonatal gut barrier and breast milk as well as the factors associated with the feeding of breast milk. Full-term newborn rabbits were assigned to one of four groups: formula-fed (group I), fed with colostrum plus formula (group II), breast-fed with breast milk (group III), and fed with colostrum plus stored breast milk (group IV). At 7 days of age, body weights were obtained, the rabbits were killed, and the mesenteric lymph nodes (MLN), liver, and spleen were quantitatively cultured for translocating bacteria. The cecum was cultured for aerobic and anaerobic enteric organisms. Distal ileal tissues were examined by light and transmission electron microscopy and compared among groups. The viability of cells in the stored, frozen breast milk was assessed by Trypan blue staining. Group I rabbits had significantly lower mean body weights compared with the other groups. The animals breast-fed breast milk had no BT to the MLN or liver and had a 9% incidence of BT to the spleen. There was no difference between BT in groups III and IV. The stored breast milk contained no viable cells. The incidence of BT to all three areas was significantly lower than in groups I and II. The animals fed with formula alone had the highest incidence of BT to the MLN (88%), liver (60%), and spleen (32%). BT in this group was significantly higher compared with groups III and IV. Rabbits fed colostrum plus formula also had a high incidence of BT to all sites. Klebsiella sp was cultured in all but the breast-fed animals. The total number of bacteria that grew in the cecum was significantly higher in the formula-fed groups than in the breast-fed groups. Structural integrity was demonstrated in the ileal specimens from all groups. There were subtle mucosal changes in the formula-fed animals. Breast milk (fresh or stored), but not colostrum, somehow enhances the barrier defense function of the neonatal gastrointestinal tract. This effect occurs independent of the maternal environment and without viable cells in the stored milk. The combination of the newborn rabbit, controlled diets, and careful culture techniques provide an effective model for the study of gut barrier function.