Time Course of Spontaneous Bacterial Translocation from Gastrointestinal Tract and Its Relationship to Intestinal Microflora in Conventionally Reared Infant Rats

Whereas the developed gut mucosal barrier prevents luminal bacteria from invading the host, bacterial translocation appears to be facilitated in the neonate. The aim of this study was to determine the extent to which bacteria spontaneously translocate from the gut to extraintestinal organs during the neonatal period and to relate translocation to the evolving intestinal flora in the rat. Newborn Sprague-Dawley rats suckled ad libitum and ate regular chow after weaning. A total of 167 rats were killed either immediately or at 1, 9, 14, 21, 26, or 42 days after delivery. Mesenteric lymph nodes (MLN), liver, heart blood, and the terminal ileal loop were harvested under sterile conditions and analyzed for aerobic and facultatively anaerobic bacteria by standard microbiologic procedures. Bacterial translocation to the MLN and liver began soon after birth and peaked during the second week. On day 14, translocation to any organ was present in 85% of rats. All cultures from the liver were sterile after day 26. By contrast, the fall in translocation to the MLN was incomplete, as 50% of pups still had positive MLN on day 42. Blood cultures were positive in three of the 167 rats. The intensity of translocation as determined by the number of organs infected significantly increased with the number of gram-negative enterics and gram-positive cocci in the gut and was negatively correlated with the percentage of lactobacilli from the total measured intestinal flora (P < 0.0001). In conclusion, bacterial translocation from the gut is a physiological and age-dependent phenomenon in the neonatal rat. Translocation appears to be facilitated when intestinal concentrations of gram-negative enterics and gram-positive cocci are high and when the concentration of lactobacilli is low.