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2001 Ocular Microbiology and Immunology Group, Abstract 5

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Corneal Lesions Produced by Fungal Extracellular Products
K. Rishi1 C.M. Kalavathy2, Kaliamurthy2 and P.A. Thomas2
1Baylor College of Medicine, Houston , TX and 2Joseph Eye Hospital, Tiruchirapalli, India

Purpose: To characterize the comeal lesions occurring in an experimental model following inoculation of crude extracelluler products of fungi (Aspergilus flavus, Candida albicans, Curvularia geniculata, fusarium solani and Lasiodiplodia theobromae) isolated from patients with fungal keratitis.

Methods: Crude filtrates of 7-day old cultures of the fungi grown in neutral Saboraud dextrose broth (NSDB) were first screened in vitro for proteolytic activity on agar plates containing casein, gelatin or collagen. These were then inoculated into freshly enucleated goat's eyes and evaluated for six hours. Additional sets of freshly enucleated goat's eyes which served as negative controls were inoculated with sterile NSDB alone or heat-inactivated culture filtrate or were left inoculated.

Results: Gelatin zymography revealed predominantly metalloprotease activity in the filtrates. Gross bulging, thinning and opacification were observed in all the test corneas; histological studies revealed damage to the epithelium and endothelium, separation of collagen fibrils in the stroma, but no polymorphonuclear leucocytes were seen. No such gross or histological alterations were seen in any of the negative controls. In general, the effects produced by filtrates of A. flavus and F. solani appeared to be more pronounced than those produced by filtrates of C. albicans C. geniculata or L. theobromae.

Conclusions: Extracellular proteases produced by fungi may be involved in tissue damage in fungal keratitis, but this hypothesis requires further evaluation.

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