Abstract
Purpose :
Bacterial endophthalmitis is a devastating infection that can cause blindness due to inflammation and retinal function loss following the introduction of organisms into the posterior segment of the eye. Unlike endophthalmitis with other bacterial pathogens, over half of Bacillus endophthalmitis cases result in significant vision loss, and the majority of these eyes are enucleated. Bacillus produces many virulence factors in the eye which may contribute to retinal damage and the bacteria’s rapid growth in the vitreous. This study analyzed the role of a putative virulence factor, Immune inhibitor A1 (InhA1), in the eye during experimental infection. InhA digests extracellular matrix proteins and contributes to circumvention of the immune response. Because InhA is highly expressed in Bacillus-infected mouse eyes during infection, we hypothesized that InhA contributes to the pathogenesis of endophthalmitis.
Methods :
We analyzed the progress of experimental endophthalmitis in mouse eyes infected with 100 CFU of B. thuringiensis wild type (WT) or its InhA1-deficient mutant (ΔInhA1). Infections were analyzed from 0-12 h postinfection by quantifying intraocular bacilli, assessing retinal function loss by electroretinography, and examining inflammation by histology. In vitro growth, hemolysis, proteolysis, and motility phenotypes of both strains were also compared.
Results :
There was no difference in hemolytic activity, however Bt ΔInhA1 proteolysis was significantly decreased, and motility and in vitro growth increased (p<0.05, 6 h) relative to WT. Infected eyes contained greater numbers of ΔInhA1 than eyes infected with WT Bt during the infection (p≤0.05). However, eyes infected with ΔInhA1 experienced a loss in retinal function that was not significantly different compared to WT-infected eyes (p≥0.05, 6-12 h). At 8 h postinfection, significant accumulation of inflammatory cells in the posterior segment were observed in the eyes infected with ΔInhA1 Bt, but not in eyes eyes infected with WT Bt. At 12 h pi, WT and ΔInhA1-infected eyes were severely inflamed with detached retinas.
Conclusions :
Without InhA1, Bt replicates faster and is less proteolytic compared to the WT. These findings may relate to subtle changes in intraocular growth and infection course of Bacillus endophthalmitis. Further experiments will explore how InhA1 affects innate immune recognition and acute inflammation in endophthalmitis.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.