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Md Huzzatul Mursalin, Phillip S Coburn, Erin Livingston, Agnès Fouet, Michelle C Callegan; Absence of S-layer impacts pathogenesis of Bacillus endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6410.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the hypothesis that Bacillus S-layer protein (SLP) contributes to the pathogenesis of endophthalmitis, a rapidly blinding infection.
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).
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.
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.
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