Keratitis due to Aspergillus flavus: Clinical profile, molecular identification of fungal strains and detection of aflatoxin production

摘要

Purpose: To document the clinicalprofile of patients with keratitis due to Aspergillus flavusand to elaborate on differences in the aflatoxin-producing potential ofkeratitis strains versus environmental strains of A. flavus. Methods: Over a 6-month period, strainsof Aspergillus flavus were isolated in culture from cornealscrape or biopsy material of patients who presented with suppurativekeratitis (clinical isolates). The strains were confirmed to be A.flavus by molecular methods (amplification of the internaltranscribed spacer 2 [ITS 2] region and direct sequencing followed bycomparative GenBank analysis). The aflatoxin-producing potential ofeach strain was determined by thin-layer chromatography. The ability ofeach strain to form sclerotia in Czapek-Dox agar (CDA) after 7 daysincubation at 30 °C in the dark and to produce a beige ring inyeast extract sucrose agar supplemented with methyl β-cyclodextrin andsodium desoxycholate (YESD medium) after 3 days incubation at30 °C was also assessed. For comparison, the tests were also runon 10 strains of A. flavus (identity confirmed by molecularmethods) collected from local farming areas (environmental isolates). Results: Aflatoxin B1 was detected in 16(80%) of 20 culture filtrate or mycelial homogenate samples of theclinical isolates (mean concentration: 366.7±125.4 parts per billion[ppb]) but in only eight (40%) of 20 samples of environmental isolates(mean concentration: 306.6±125.4 ppb). Seven of the eightaflatoxin-producing clinical isolates and two of the fouraflatoxin-producing environmental isolates formed sclerotia (400μm) and a beige ring in culture. Conclusions: Aflatoxin B1 was detectedin a significantly higher percentage of growth samples of clinicalisolates (80%) than growth samples of environmental isolates (40%) (χ2=6.667;p=0.0098); the therapeutic implications of this finding require furtherstudy. The production of sclerotia and a beige ring in culture appearto be useful markers of aflatoxin-producing potential in strains of A.flavus isolated from keratitis.