Development of a guinea pig model of chorioamnionitis and fetal brain injury

Objective The purpose of this study was to develop a guinea pig model of chorioamnionitis to study the mechanisms that lead to fetal brain injury. Study design Pregnant guinea pigs at 70% gestation were inoculated intracervically with 1000 to 2500 colony-forming units of Escherichia coli. Guinea pigs were killed 2 to 3 days after bacterial inoculation. Maternal blood and fetal amniotic fluid samples were analyzed for proinflammatory cytokine tumor necrosis factor–α, interleukin-1β, and interleukin-6 levels with the use of enzyme-linked immunosorbent assay kits. Fetal brains were stained for evidence of cell death with NeuroTacs stain. Results Of 34 maternal guinea pigs that were given an intracervical inoculation of E coli, 8 guinea pigs showed microbiologic evidence of chorioamnionitis in the amniotic fluid. Tumor necrosis factor–α and interleukin-6 were significantly higher (P<.05) in amniotic fluid samples that were obtained from sows that were subjected to intracervical inoculation with bacteria as compared with control animals (n = 6 control maternal animals). These results were observed even if no bacteria were found subsequently on culture of the amniotic fluid from inoculated animals, which indicated that indirect exposure to infectious agents was sufficient to cause an elevated inflammatory response in the fetus. Levels of white matter injury were greater in fetuses that were exposed to bacterial infection in utero, as compared with control animals (P<.05). This result was found in the staining of periventricular and cortical white matter for the immunolabeling of activated caspase 3 and NeuroTacs staining for cells that exhibited evidence of apoptotic cell death (positive stain with evidence of karyorrhexis). Conclusion Intracervical inoculation with E coli results in chorioamnionitis in guinea pigs that is associated with fetal brain injury.