Gut-derived bone infection in the neonatal rat

Abstract

The risk of osteomyelitis is increased in the premature and critically ill neonate. Although potential sites of bacterial entry are present in many of these infants, the source of infection frequently cannot be established. This study was performed to assess the possible role of bacterial translocation from the intestine in the origin of bone infection using models of breast-fed and formula-fed rat pups. Newborn Sprague-Dawley rats suckled either ad libitum by the dam (n = 30), or were fed a rat milk-simulated formula (n = 30). After 3 d, the animals were killed, and the left femur, heart blood, mesenteric lymph nodes, liver, spleen, and terminal ileum were excised. Organs were analyzed for bacteria by standard microbiologic procedures. Bacterial translocation occurred in 23% of breast-fed rats; the bone was not infected in any of these animals. After feeding of formula diet, bacterial counts of the ileum were markedly elevated (p < 0.001), and the composition of the gut flora was disrupted. Bacterial translocation was noted in all formula-fed rats. Bone cultures were positive in 23 of 30 (77%) rats after formula-feeding (p < 0.001 versus breast-feeding). Organisms translocated to the bone included Enterococci, Proteus, Enterobacter, and Escherichia coli. Bacterial species cultured from the bone correlated with the individual colonization pattern of other extraintestinal organs and with the composition of the ileal flora. Members of the gut flora can escape the intestine and colonize the bone in formula-fed rats. The gut should be considered as a potential source for osteomyelitis in the neonate.