Determinant of bacterial translocation in the newborn: Small bowel versus large bowel colonization

Abstract

This study investigated the relationship between bacterial translocation (BT) and small and large bowel bacterial colonization in the neonatal rabbit. The authors have previously shown that spontaneous BT occurs in rabbits during the first week of life, but is less frequent before the third day of life. The authors have also shown that bacterial colonization of the small bowel is delayed until 3 to 5 days of age, and is preceded by colonization of the large bowel. Therefore, the authors hypothesized that BT is dependent on small bowel, not large bowel, colonization. New Zealand White rabbit pups (n = 255) were divided into four groups, formula-fed (FF), formula-fed plus antibiotic (FFAB), breast-fed (BF) and unfed controls (UC). Animals from each group were killed on day 1 to 4 of life. Small bowel (SB) and large bowel (LB) specimens, mesenteric lymph nodes (MLN), spleen (SPL), and liver (LIV) were obtained from each rabbit, incubated for 24 hours in thioglycolate broth, and plated on both MacConkey and Colistin Naladixic Acid media in an aerobic environment. After 24 hours, growth on either plate was recorded. Bacterial colonization was significantly greater in FF versus UC, BF, and FFAB rabbit groups. In addition, large bowel colonization was significantly increased compared with small bowel colonization in all feeding groups ( P < .05). Bacterial translocation to MLN, SPL, and LIV ranged from 10% to 27% in all groups. Gram-negative bacteria predominated over gram-positive bacteria in translocation to the various tissues sampled. The ratio of gram-negative to gram-positive bacteria was greater in the UC, FF, and FFAB groups compared with that of the BF rabbit group. Bacterial translocation to all tissues in all feeding groups was significantly correlated with small bowel bacterial colonization ( P < .05). The incidence of bacterial translocation to MLN in small bowel positive rabbits was significantly decreased in the BF group compared with the FF and FFAB groups at 3 days of age. The authors conclude the following: (1) Bacterial translocation almost always requires small bowel colonization. Colonization of the large bowel alone rarely leads to translocation if the small bowel is sterile. (2) Enteral antibiotics had no effect on bacterial translocation. (3) These findings may explain why necrotizing enterocolitis and neonatal sepsis do not occur during the first 3 to 5 days of life when small bowel bacterial colonization is absent.