Identification of Filamentous Fungi Isolated from Clinical Samples by Two Different Methods and Their Susceptibility Results

Molds are widely distrubuted in nature. Aspergillus spp. represent the most frequently observed causative agents, however less frequent pathogens Fusarium, Scedosporium and Zygomycetes have also been considered the most important causes of morbidity and mortality in profoundly immunosuppressed hosts. The aims of this study were to identify filamentous fungi isolated from clinical specimens by conventional and molecular methods, and to detect their antifungal susceptibilities. A total of 6742 clinical specimens obtained from hospitalized patients at critical units of Mersin University Medical Faculty Hospital and sent to our laboratory between April 2008-January 2010 were included in the study. The isolates were identified by classical mycological methods and polymerase chain reaction-based DNA sequencing. Susceptibilities to fluconazole and voriconazole were tested by disk diffusion method and to fluconazole, voriconazole, amfoterisin B, caspofungin and posaconazole by E-test. Filamentous fungi were isolated from 71 (1.05%) samples (13 sputum, 4 wound, 4 peritoneal fluid, 3 extrenal ear discharge, 3 abscess and one of each cerebrospinal fluid, blood, tissue biopsy, nasal swab and conjunctival swab) which belonged to 32 patients (13 female, 19 male; age range 7 months-77 years, mean age: 46.6 years). Of the patients 62.3% presented one or more risk factors such as chronic renal failure (n=8), chronic obstructive lung disease (n=6), malignancy (n=6), diabetes mellitus (n=5) and peripheral vascular disease (n=5). Of the isolates six were identified as Aspergillus niger, six as Aspergillus flavus, five as Aspergillus fumigatus, four as Aspergillus terreus, five as Fusarium spp., two as Bipolaris spp., and one of each as Acremonium spp., Aurebasidium spp., Mucor spp., and Scedosporium spp. By conventional methods. Three isolates exhibited different identities by DNA sequencing. All Aspergillus isolates were correctly identified at species level by both methods, Other fungi were identified at genus level by conventional methods and at species level by DNA sequencing. Fluconazole minimum inhibitory concentration (MIC) values were determined as > 256 mg/L in all strains, except Scedosporium; voriconazole MIC values were < 0.38 mg/L in all Aspergillus spp. Caspofungin MIC values were > 32 mg/L for Fusarium, Scedosporium, Rhizopus and Bipolaris strains and <= 0.006-0.125 mg/L in all Aspergillus isolates, In three strains (Fusarium equiseti, Cylindrocarpon lichenicola and Rhizopus oryzae) posaconazole minimum inhibitory concentration (MIC) values were > 32 mg/L, however it was < 1.5 mg/L, for the other strains. Amphotericin B MIC values were > 32 mg/L for Fusarium, Scedosporium, Rhizopus and all A.terreus strains and < 2 mg/L for the others. E-test and disk diffusion test results were compatible with each other for all the antifungal agents tested. In conclusion, the identification of filamentous fungi such as Aspergillus and Fusarium spp. is easily and reliably achieved by conventional methods. Since the rate of invasive fungal infections is increasing currently, filamentous molds should be searched especially in the clinical specimens of immunocompromised patients for accurate and prompt diagnosis of such infections and to decrease the related mortality risk.