Fungal Spectrum Identified by a New Slide Culture and In Vitro Drug Susceptibility Using Etest in Fungal Keratitis

Abstract

Purpose: To investigate the spectrum of fungal species causing keratitis and to test antifungal drug susceptibility to each isolate using Etest. Methods: Microbial cultures were performed for patients who were clinically diagnosed with fungal keratitis between September 2002 and July 2004. Modified slide culture was established to identify the fungal species of the isolates. Etest (AB BIODISK, Solna, Sweden) was applied to determine the antifungal agent susceptibility of each isolate to itraconazole, fluconazole, and amphotericin B in vitro, respectively. Results: Among 73 eyes of 73 patients with clinical diagnosis of fungal keratitis, 61 strains of fungi were isolated from 61 eyes. The rate of positive culture was 81.3% of all cases. The spectrum of fungal species involved: 58 (95.1%) isolates of filamentous fungi, including the two most common genera—Fusarium (n = 33, 54.1%) and Aspergillus (n = 9, 14.8%),—followed by 16 (26.2%) isolates of other genera of filamentous fungi such as Alternaria (n = 3, 4.9%), Trichophyton (n = 3, 4.9%), Curvularia (n = 2, 3.3%), Chrysosporium (n = 2, 3.3%), Acremonium (n = 2, 3.3%), and Scedosporium (n = 1, 1.6%), 1 (1.6%) yeast of Candida, as well as two (3.3%) dimorphic fungi of Blastomyces and Sporothrix isolate each. Three filamentous fungi of the isolates failed to be identified according to the information provided by slide culture. The results of Etest showed that 20 (60.6%) isolates of Fusarium were susceptible to amphotericin B, whereas all of them were resistant to itraconazole and fluconazole. All nine (100%) isolates of Aspergillus were sensitive to itraconazole, whereas four (44.4%) of them were sensitive to amphotericin B, and only two (22.2%) of them were sensitive to fluconazole. Seventeen (89.5%), 13 (68.4%), and 10 (52.6%) isolates of the remaining 19 organisms were sensitive to amphotericin B, itraconazole, and fluconazole, respectively. Conclusions: Fusarium and Aspergillus are the most frequent pathogenic organisms in causing fungal keratitis, whereas other species of fungi can also cause corneal infection. In vitro Etest for assessing antifungal drug susceptibility is a simple and practical method and may provide referential information for clinical consideration of choosing antifungal agents to treat fungal keratitis.

KEYWORDS:

• Etest
• fungal identification
• fungal keratitis
• fungal spectrum
• modified slide culture