Differentiating Ocular Pathogenic Staphylococcus epidermidis Isolates Using a Human Corneal Epithelial Cell Coculture Model.

Purpose: To develop an in vitro human corneal epithelial cell (HCEC) coculture model for differentiating pathogenic from nonpathogenic ocular Staphylococcus epidermidis isolates. Methods: HCECs were cocultured with S. epidermidis strains (104-108 CFU/mL) for 12 to 72 hours. Cell viability was assessed using calcein AM staining. Seventeen strains were evaluated in this model and validated in mouse keratitis models. Cytotoxicity profiles of pathogenic versus nonpathogenic strains were compared, and receiver operating characteristic analysis was performed to evaluate HCEC viability as a predictor of pathogenicity. Results: A 24-hour HCEC coculture assay reliably quantified bacterial cytotoxicity across concentrations. In vivo, 12 of 17 strains (70.6%) were pathogenic in mouse keratitis models. In vitro, cytotoxicity was detected in 50.0% of pathogenic strains (6/12) at 104 CFU/mL, 58.3% (7/12) at 105 CFU/mL, and 83.3% (10/12) at 106 CFU/mL, whereas no nonpathogenic strains induced cytotoxicity at ≤106 CFU/mL. At 106 CFU/mL, HCEC viability was significantly lower with pathogenic than nonpathogenic strains (P = 0.006). Receiver operating characteristic analysis identified a 91.36% viability cutoff at 106 CFU/mL of S. epidermidis to distinguish pathogenic strains, yielding an area under the receiver operating characteristic curve of 0.9167, with 100% specificity and 91.7% sensitivity. Conclusions: This HCEC coculture assay provides a rapid and reliable method to distinguish pathogenic from nonpathogenic S. epidermidis ocular isolates, with strong concordance with in vivo keratitis outcomes. Translational Relevance: This model offers a practical diagnostic tool to identify clinically relevant S. epidermidis strains, supporting earlier and more accurate diagnosis of bacterial keratitis and guiding targeted therapy.