Effects of Bacillus growth and toxin production on retinal pigment epithelium cells in vitro.

Abstract

Abstract: : Purpose: To investigate the cytopathological effects of Bacillus growth and toxin production on retinal pigment epithelial cells in vitro. Methods: Human retinal pigment epithelial cells (RPEs) were inoculated with a wild type toxin–producing B. cereus strain (ATCC 14579), or an isogenic quorum sensing toxin–defective mutant (plcR–). RPEs were inoculated with 10², 10³, 10⁴, or 10⁵ cfu/ml of wild type or plcR– B. cereus. At various times post–infection, RPEs were analyzed for bacterial growth, membrane integrity (lactate dehydrogenase release), and cell viability (trypan blue exclusion). The extent of inflammatory cytokine gene expression and production was analyzed using real–time PCR and ELISA, respectively (IL–6, TNFα, MIP–1α, and IL–1α). Results: The rate of RPE membrane leakage upon exposure to Bacillus was dose and time dependent, but not strain dependent. The rate of RPE death was dose, time, and strain dependent, with wild type Bacillus causing death more rapidly than the atoxigenic quorum sensing mutant. Bacillus exposure also caused RPEs to express and produce IL–6. Conclusions: The results demonstrate the deleterious effects of Bacillus growth and toxin production on RPE cells. Interactions between Bacillus, its toxins, and the RPE could contribute to blood–retinal barrier perturbation and the explosive inflammatory response during endophthalmitis. The relationship of these findings to the pathogenesis of Bacillus endophthalmitis is presently being investigated.

Keywords: bacterial disease • endophthalmitis • retinal pigment epithelium