Staphylococcus aureus pore-forming toxins differentially shape disease severity in experimental endophthalmitis

Ocular infections caused by Staphylococcus aureus result in poor visual outcomes due to the expression of numerous virulence factors during infection. We hypothesized that pore-forming toxins (PFTs) contribute to the pathogenesis of S. aureus endophthalmitis, a severe intraocular infection that can result in blindness. We analyzed infection outcomes using wild-type (LAC), PFT-null (LAC ΔΔΔΔΔ), leukocidin-null (LAC Δleukocidin), or alpha toxin-deficient (LAC Δhla) mutants. These strains exhibited no differences in growth in brain heart infusion (BHI) and explanted rabbit vitreous. The expression of PFT genes was detected in both environments, but transcript levels were less in vitreous relative to that of BHI. Experimental endophthalmitis was induced in C57BL6/J mice by intravitreal injections of 5,000 colony-forming units (CFU) of S. aureus LAC or one of its three mutants. To quantify infection severity, eyes were analyzed for retinal function, intraocular CFU, inflammation via myeloperoxidase (MPO), cytokines and chemokines, neutrophil infiltration, alpha toxin production, and gross pathology via histology and slit-lamp imaging. Infections with LAC ΔΔΔΔΔ or LAC Δhla resulted in improved retinal function, reduced intraocular CFUs, decreased ocular damage, and a trend toward decreased inflammation compared to infections with LAC. In contrast, infections with LAC Δleukocidin progressed similarly as infections with LAC. Increasing concentrations of alpha toxin were detected over time in the eyes infected with LAC and LAC Δleukocidin; 40%-60% of infiltrating neutrophils were ADAM10⁺, identifying these cells as potential targets for alpha toxin. Collectively, these results suggest that alpha toxin may be the main PFT driving the severity of S. aureus endophthalmitis.