DESCRIPTIONS OF MEDICAL FUNGI
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14<br />
Descriptions of Medical Fungi<br />
Aspergillus flavus complex<br />
Aspergillus section Flavi historically includes species with conidial heads in shades<br />
of yellow-green to brown and dark sclerotia. Hedayati et al. (2007) reviewed the A.<br />
flavus complex and included 23 species or varieties, including two sexual species,<br />
Petromyces alliaceus and P. albertensis. Several species of section Flavi produce<br />
aflatoxins, among which aflatoxin B1 is the most toxic of the many naturally occurring<br />
secondary metabolites produced by fungi. Aflatoxins are mainly produced by A. flavus<br />
and A. parasiticus, which coexist and grow on almost any crop or food (Varga et al.<br />
2011). Within the complex, A. flavus is the principle medically important pathogen of<br />
both humans and animals. However, some other species in the A. flavus complex,<br />
notably A. oryzae, A. avenaceus, A. tamari, A. alliaceus and A. nomius, may cause<br />
rare mostly superficial infections (Hedayati et al. 2007, de Hoog et al. 2015).<br />
Note: Accurate species identification within A. flavus complex remains difficult due<br />
to overlapping morphological and biochemical characteristics. For morphological<br />
identifications, it is recommended to report as Aspergillus flavus complex.<br />
Molecular Identification: ITS sequence analysis is sufficient to identify to species<br />
complex level only. Definitive identification requires analysis of β-tubulin, calmodulin<br />
and actin genes (Samson et al. 2007, Balajee et al. 2005a).<br />
Aspergillus flavus Link ex Grey<br />
Aspergillus flavus has a worldwide distribution and normally occurs as a saprophyte in soil<br />
and on many kinds of decaying organic matter, however, it is also a recognised pathogen<br />
of humans and animals. It is a causative agent of otitis, keratitis, acute and chronic<br />
invasive sinusitis, and pulmonary and systemic infections in immunocompromised<br />
patients. A. flavus is second only to A. fumigatus as the cause of human invasive<br />
aspergillosis (Hedayati et al. 2007).<br />
RG-2 organism.<br />
Morphological Description: On Czapek Dox agar, colonies are granular, flat, often<br />
with radial grooves, yellow at first but quickly becoming bright to dark yellow-green with<br />
age. Conidial heads are typically radiate, later splitting to form loose columns (mostly<br />
300-400 µm in diameter), biseriate but having some heads with phialides borne directly<br />
on the vesicle (uniseriate). Conidiophore stipes are hyaline and coarsely roughened,<br />
often more noticeable near the vesicle. Conidia are globose to subglobose (3-6 µm in<br />
diameter), pale green and conspicuously echinulate. Some strains produce brownish<br />
sclerotia.<br />
Key Features: Spreading yellow-green colonies, rough-walled stipes, mature vesicles<br />
bearing phialides over their entire surface and conspicuously echinulate conidia.<br />
Antifungal Susceptibility: A. flavus complex (Australian National data); MIC µg/<br />
mL.<br />
No 16<br />
AmB 68 1 5 7 30 22 3<br />
VORI 68 1 1 6 25 24 11<br />
POSA 57 2 1 5 16 26 7<br />
ITRA 68 1 3 11 43 10