Abstract
OBJECTIVE: The research aims to elucidate the pathogenic mechanisms of Candida parapsilosis infection after keratoplasty and provide evidence-based guidance for the clinical management of Candida infections in ophthalmic practice. METHOD: Biofilms were cultured from 45 strains of Candida. The total biomass of the biofilms was measured using the crystal violet staining method, and the biofilm activity was assessed via the XTT reduction assay. Cell surface hydrophobicity and adhesion were evaluated for all Candida strains. The minimum inhibitory concentration (MIC) of planktonic Candida was determined using the colorimetric microbroth dilution method, while the MIC of biofilm-embedded Candida was measured via the XTT reduction assay. The release of 1, 3-β-D-glucan was detected using the G-test, and the chemotactic ability of 1, 3-β-D-glucan on neutrophils was evaluated via the Transwell assay. Molecular typing of Candida parapsilosis was performed using microsatellite genotyping. Statistical analysis was conducted using the Kruskal-Wallis (K-W) test. RESULTS: In 45 postoperative ocular Candida isolates, Candida parapsilosis accounted for 48.9% (22/45), Candida albicans 35.6% (16/45), Candida tropicalis 11.1% (5/45), and Candida glabrata 4.4% (2/45). The total biofilm biomass and metabolic activity of Candida parapsilosis at 4°C were significantly higher than those of the other Candida species. In the cell surface hydrophobicity assay, Candida parapsilosis was more hydrophobic than Candida albicans and Candida glabrata, but less hydrophobic than Candida tropicalis. Among Candida parapsilosis isolates, 77.3% (17/22) showed strong adhesion ability and 81.8% (18/22) showed strong biofilm-forming ability (OD450>0.16). Candida colony and spore morphology were found to correlate with biofilm-forming ability. Strains with strong biofilm-forming ability had wrinkled, dry colonies; Gram-stained spores appeared as pseudohyphae; and lactophenol cotton blue staining showed spores that were uniformly and deeply stained. In the biofilm-antigenicity analysis, the non-biofilm-forming group's 1, 3-β-D-glucan release was significantly higher than that of the strong biofilm group, thereby attracting more neutrophils. In antifungal susceptibility tests, except for C. tropicalis, biofilm-grown Candida showed higher minimum inhibitory concentrations (MICs) than planktonic cells for all antifungal drugs. Caspofungin was active against all isolates in both states. CONCLUSIONS: This study demonstrates that C. parapsilosis has greater adhesion ability and a stronger capacity to form biofilms at 4°C (with higher metabolic activity) than other Candida species. When laboratory findings reveal a Candida isolate with a rough colony morphology, its biofilm-forming ability should be tested and antifungal susceptibility should be assessed under biofilm-growing conditions rather than in planktonic culture.Clinically, we recommend shifting antifungal therapy to caspofungin for such infections.