Identification of Aspergillus Species Using Morphological Characteristics

Objectives: Although molecular methods continue to improve and become more rapidly available, microscopy and culture remain commonly used and essential tools for identification of Aspergillus spp. In this study we emphasize on morphological methods including; macroscopic and microscopic characteristics for identification of Aspergillus species isolated from environmental and clinical specimens. Methodology: We used four differential media: czapek dox agar (CZ), czapek yeast agar (CYA), malt extract agar (MEA), and czapek yeast 20% sucrose agar. Morphological features of colonies on above culture media as well as microscopically characteristics for the major strains were studied and then compared with those of standard Aspergillus strains. Our major subjects were Iranian Aspergillus strains isolated from clinical and environmental specimens. Standard Aspergillus strains for study development included; A. fumigatus, (JCM 10253), A. flavus (JCM 2061), A. niger (JCM 10254), A. nidulans (JCM 02728), A. tereus (JCM 10227). Morphological features of Aspergillus cultures were studied, the major and remarkable macroscopic features in species identification were the colony diameter, color (conidia and reverse), exudates and colony texture. Microscopic characteristics for the identification were conidial heads, stipes, color and length vesicles shape and seriation, metula covering, conidia size, shape and roughness also colony features including diameter after 7 days, color of conidia, mycelia, exudates and reverse, colony texture and shape. Finally we compared the morphological characteristics of tested Aspergillus isolates with those of the standard species Results: Aspergillus isolates were identified in the level of species using the differential culture media. A total of 205 Aspergillus isolates studied included: 153(75%) environmental Aspergilli and 52 (25%) clinical isolates. Within 11 Aspergillus species identified, A.flavus (55%), A.niger (31.7%) and A. fumigatus (8.7%) were the most common Aspergillus isolates from all of the specimens. Conclusion: In our view morphological method using the differential media is the most reliable and sensitive assay to identify more medically important Aspergillus species.