Aspergillus fumigatus complex
Aspergillus section Fumigati includes species characterised by uniseriate aspergilla with columnar conidial heads in shades of blue-green and flask-shaped vesicles (Raper and Fennell, 1965). Teleomorphic species belonging to the “Aspergillus fischeri series” of the A. fumigatus group (Raper and Fennell, 1965) were placed in the genus Neosartorya (family Trichocomaceae) by Malloch and Cain (1972). Section Fumigati includes more than 23 Neosartorya species and 10 anamorphic species (Samson et al. 2007).
Although A. fumigatus is recognised as the major human pathogen within the complex, recent phylogenetic studies have demonstrated that some human and animal infections may be caused by A. lentulus, A. fumigatiaffinis, A. fumisynnematus, A. felis, Neosartorya fischeri, N. pseudofischeri, N. udagawae, N. hiratsukae and N. spinosa (Coriglione et al. 1990; Summerbell et al. 1992; Padhye et al. 1994a; Lonial et al. 1997; Jarv et al. 2004; Balajee et al. 2005, 2006; Barrs et al. 2013).
Four species in the Aspergillus fumigatus complex showing overlapping morphological characteristics; (a) Aspergillus fumigatus, (b) Aspergillus lentulus, (c) Neosartorya fischeri and (d) Aspergillus felis.
Aspergillus fumigatus Link ex Grey
Morphological Description: On Czapek Dox agar, colonies are typically blue-green with a suede-like surface consisting of a dense felt of conidiophores. Conidial heads are typically columnar (up to 400 x 50 µm but often much shorter and smaller) and uniseriate. Conidiophore stipes are short, smooth-walled and have conical-shaped terminal vesicles which support a single row of phialides on the upper two thirds of the vesicle. Conidia are produced in basipetal succession forming long chains and are globose to subglobose (2.5-3.0 µm in diameter), green and finely roughened. Note: This species is thermotolerant with a maximum growth temperature of 55C.
Key Features: Uniseriate and columnar conidial heads with the phialides limited to the upper two thirds of the vesicle and curving to be roughly parallel to each other.
Molecular Identification: Sequence analysis of ITS is sufficient to identify to species complex level only. For definitive identification analysis, β-tubulin, calmodulin and actin genes is required (Samson et al. 2007; Balajee et al. 2005).
Culture of Aspergillus fumigatus.
Conidial head of A. fumigatus
(Note: uniseriate row of phialides on the upper two thirds of the vesicle).