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43: Effect of stress and of formula feeding on the acquisition of intestinal flora in newborn rats

In a rat model of neonatal necrotizing enterocolitis, breast milk, and most specifically milk macrophages have been shown to be protective to the susceptible stressed rat. Moreover, it was found that the affected animals died with enterobacterial septicemia. (Ped. Res. 1974, V. 8, p. 110). In order to batter define the role of the gastrointestinal flora in this disorder, the kinetics of their establishment in the stressed and unstressed newborn rat were determined as a function of feeding. Newborn rats were fed whole breast milk, frozen breast milk, formula and formula with peritoneal macrophages. They were studied on days 1, 3, and 7 following birth. The gut was divided into duodenum-jejunum, ileum-cecum, and colon. These portions of gut were homogenized and quantitative cultures of aerobic and anaerobic flora were performed. Stress alone appeared to favor the establishment of enterobacterial flora, this effect being most dramatic in the duodenum-jejunum. Sterile milk formula and frozen rat milk fed rats had a greater level of enterobacterial colonization than nursed rats or rats fed the formula plus peritoneal macrophages. Thus these leukocytes, which can be demonstrated to be viable in the stomach and jejunum, protect against colonization with enteric bacteria in vivo. Whether they protect through their demonstrated bactericidal activity or through other mechanisms remains to be determined.