Abstract
Purpose :
To investigate the hypothesis that Bacillus S-layer protein (SLP) contributes to the pathogenesis of endophthalmitis, a rapidly blinding infection.
Methods :
Wild-type (WT) and S-layer deficient (△slpA) Bacillus thuringiensis (B. thuringiensis) were compared for differences in phenotype and virulence. Endophthalmitis was induced in C57BL/6J mice by intravitreally injecting 100 cfu WT or △slpA B. thuringiensis. Infected eyes were analyzed by bacterial counts, retinal function analysis, histology, and neutrophil influx. Values represent N≥5, mean ± SEM. Nuclear proteins from human retinal Muller cells (MIO-M1) cells were extracted after treatment with SLP (10 µg/mL) and NF-kB activation was measured by ELISA. Total RNA was extracted from MIO-M1 cells treated with SLP (10 µg/mL ) or PBS for 10 hours and real-time qPCR was performed to examine the expression of inflammatory cytokines (IL-6, TNFα) and chemokines (CXCL-1, CCL2).
Results :
Phenotypes were similar in WT and △slpA strains. The replication and localization of WT and △slpA B. thuringiensis in mouse eyes was similar. At 10 hours postinfection, both WT and △slpA B. thuringiensis were localized near the retina and in the anterior segment, as well as in the midvitreous. Surprisingly, the retention of retinal function in eyes infected with △slpA B. thuringiensis was greater than that of eyes infected with the WT strain at 8, 10, and 12 hours postinfection. In △slpA-infected eyes, retinas were intact, retinal layers were distinguishable, and inflammatory influx was minimal. In contrast, severe inflammation, anterior and posterior segment infiltration, and retinal detachments were observed in WT-infected eyes. Bacillus SLP was a potent stimulator of NF-κB pathway and induced the expression of proinflammatory mediators (IL6, TNFα, CXCL-1, and CCL2) in human retinal Muller cells.
Conclusions :
Taken together, our results suggest that Bacillus SLP contributes to the pathogenesis of endophthalmitis, potentially by triggering innate inflammatory pathways in the retina. Further experiments will explore how S-layer drives innate immune recognition and acute inflammation in endophthalmitis and the utility of S-layer as a therapeutic target.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.