Retinopathy associated with Enterococcus enteropathy in the neonatal rat

PURPOSE. Preretinal neovascularization has been previously observed in neon atal rats with spontaneously occurring diarrhea. This neovascularization ap pears analogous to retinopathy of prematurity (ROP), which occurs in human neonates. A new enterococcus species, designated Enterococcus rattus, has b een isolated from the duodenum of these rats. In the present controlled stu dy, the effect of the enteropathy induced by this organism on the retinal v asculature in the neonatal rat was further investigated. METHODS. One hundred fifty newborn Sprague-Dawley rats were randomly assign ed to 6 expanded litters (n = 25). On the second day of life, animals were gavaged with either 100 mu l of E. rattus suspension (1.0 x 10(7) colony fo rming units, inoculated group, n = 100 rats) or 100 mu l saline (control gr oup, n = 50 rats). ALI rats were raised in room air and were killed on day 13 of life. Duodenal and blood samples were cultured. The retinal vasculatu re was assessed using fluorescent microscopy and ADPase staining in a maske d manner. Two additional inoculated litters and one control litter were stu died for evaluation of arterial blood gases and validation of the grading m ethod for preretinal neovascularization. RESULTS. One hundred percent of rats in the inoculated group developed seve re diarrhea and had duodenal cultures positive for E, rattus compared with 0% in the control group. Preretinal neovascularization similar to ROP occur red in 55% of rats in the inoculated group compared with 2% in the control group (P = 0.001). Retinal vascular areas were reduced in the inoculated gr oup (mean +/- SD, 89% +/- 5% versus 96% +/- 2%; P < 0.001). Rats in the ino culated group demonstrated severe growth retardation (final weight, 9.7 +/- 2.2 versus 16.7 +/- 2.7 g, P < 0.001). Inoculated animals also experienced acidosis (pH 7.31 +/- 0.06 versus 7.39 +/- 0.06 control, P = 0.04). CONCLUSIONS. A previously undescribed enterococcal enteropathy was associat ed with preretinal neovascularization similar to ROP in the neonatal rat. T his supports an independent role for factors other than inspired oxygen in the development of ROP.