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2025 OMIG Abstract

Investigating the Combination of Salinomycin and Ophthalmic Antibiotics in Treating Bacterial Keratitis and Preventing Corneal Scarring

Rebecca Li, Collynn Woeller, Rachel Wozniak

Department of Ophthalmology, University of Rochester Medical Center, Rochester, New York

Purpose: Bacterial keratitis (BK) is a rapid, devastating corneal infection leading to over 2 million cases of blindness annually worldwide. Staphylococcus aureus and Pseudomonas aeruginosa are the primary Gram-positive and Gram-negative pathogens, respectively, associated with BK, requiring intensive antimicrobial therapy to prevent corneal damage and preserve vision. However, despite effective antimicrobial therapy, BK can still result in significant corneal scarring that often leaves patients with permanent vision loss. While topical steroids are often used to mitigate corneal scarring post-BK, their efficacy is limited. Interestingly, the antibiotic salinomycin has recently been identified as a potent anti-scarring agent in an animal model of proliferative vitreoretinopathy. Additionally, preliminary data has shown that salinomycin may potentiate three ophthalmic antibiotics: moxifloxacin, tobramycin, and erythromycin. As such, the overarching goal is to investigate the therapeutic potential of salinomycin, an antibacterial agent recently identified with potent anti-scarring activity, in combination with known ophthalmic antimicrobials to eliminate BK-infecting pathogens and simultaneously reduce BK-induced corneal scarring.

Methods: Standard laboratory strains, S. aureus UAMS-1 and P. aeruginosa PAO1, as well as 10 diverse ocular clinical isolates were used for experiments. Fractional inhibitory concentration indices (FICI) were determined and used to classify the combined antimicrobial activity of salinomycin and moxifloxacin, tobramycin, or erythromycin against all strains (FICI = MIC_comboA/MIC_aloneA + MIC/_comboB/MIC_aloneB). Bacterial kill curves and standard human cell cytotoxicity assays were performed with the indicated agents alone and in combination. Western blot was used to quantify α-smooth muscle actin (αSMA) protein expression in human corneal fibroblasts stimulated with TGF-β and 50 or 100nM of salinomycin as a proxy for myofibroblast formation.

Results: The MIC of salinomycin against S. aureus UAMS-1 and P. aeruginosa PAO1 was 2 ug/mL, and > 450 ug/mL, respectively, and 1 ug/mL and > 450 ug/mL against the clinical isolate sets of S. aureus and P. aeruginosa, respectively. The average FICI of salinomycin + moxifloxacin against the S. aureus clinical isolate set was 0.797 + 0.158 (additive), tobramycin + salinomycin 1.096 + 0.579 (neutral), and erythromycin + salinomycin 0.945 + 0.547 (additive). In contrast, the average FICI of salinomycin + moxifloxacin against the P. aeruginosa clinical isolate set was 2 + 0 (neutral), tobramycin + salinomycin 1.156 + 0.583 (neutral), and erythromycin + salinomycin 2 + 0 (neutral). Bacterial kill curves of each combination against UAMS-1 and PAO1 did not show any improved bacterial killing beyond the individual components. MTT assays revealed salinomycin cytotoxicity at concentrations above 2 ug/mL, erythromycin cytotoxicity above 0.5 ug/mL, and no cytotoxicity for moxifloxacin or tobramycin. Western blot analysis confirmed that αSMA protein levels are induced by TGF-β stimulation but are suppressed when salinomycin (50 or 100 nM) is co-administered, suggesting that salinomycin has potent anti-fibrotic effects in the cornea by blocking myofibroblast formation.

Conclusions: Together, these findings elucidate a novel role of salinomycin as an adjunctive treatment in combination with moxifloxacin, tobramycin, or erythromycin to effectively treat and mitigate corneal scarring in BK. Future experiments will address cytotoxicity of salinomycin antibiotic combinations and expand our knowledge on the immunomodulatory properties of salinomycin and its potential to reduce corneal scarring.