Church summarized all available material on the genus in a monograph.'O This led to the release of a comprehensive manual for identification," and the ultimate publication of the well-recognized textbook on the genus by Raper and Fennell." Current general reviews of this genus have been published by Austwick" and Rippon." Several pioneering reviews on the varied spectrum of clinical disorders induced by this genus have contributed a great deal to the better understanding of aspergillosis: on alIergic aspergillosis by Henderson," Pepys,16 McCarthy and Pepys, l 7 Safirstein et aI.," and Katzenstein, Liebow, and Friedrnanl9; on aspergilloma by Orie, DeVries, and Kiestra" Downloaded by [University of Otago] at 11:00 23 July 2015
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CRC Critical Reviews in Clinical Laboratory Sciencesand McCarthy and Pepys"; and on disseminated aspergillosis by Tan and Sugai" and Vogel et al.23
MYCOLOGIC CHARACTERISTICSAspergilli occur in infected tissues as branched, septate hyphae (Figure lA), but their morphology varies with increasing host resistance, from a freely expanding, branching mycelium (normal vegetative hyphae) to compact, tangled filaments ("granules") in fungal ball processes ( Figure 1B). Conidiophores and spores are sometimes seen in necrotic tissue exposed to the air ( Figure 1C). Essential characteristics of the genus are typified by the conidiophore, consisting of an elongate stalk with an inflated vesicle bearing one or two rows of sterigmata, from which emanate chains of generally spherical, one-celled conidia ( Figure 1D and Figures 2 and 3). The mycelium is septate and nonpigmented, except for the conidiophore in certain species and the spores of most species. Species are identified by color and shape of conidial heads, the presence of one or two rows of sterigmata, conidiophore length along with their color, size, and shape ( Figure 2). Colonies grow rapidly on Sabourand's dextrose agar or Czapek Solution at 25" or 37°C and initially appear as flat white and velvety to floccose in nature ( Figure 1E). Owing to the color of the spore heads, the mycelial mat usually takes on a grey-green appearance, but in some species can be tan, yellow, andin the case of A . niger,brown or black. Hyphae can be easily identified in wet mounts of sputum from patients suspected of having the disease ( Figure 1F). Specific criteria empIoyed in the identification of aspergilli are beyond the scope of this review and already well characterized. 12.13 Using a scanning electron microscope, Mullins and Harvey were able to make some interesting observations on spore formation and liberation by A . fumigatus. Development of sterigmata and spores from sterigmata was noted to be synchronous with the formation of large spore Connections between spores in a chain were noted to be of variable length, dependent on the smoothness or roughness of the spore wall.
DISTRIBUTION AND EPIDEMIOLOGYThe genus Aspergiffus is the most commonly encountered fungus in man's environment. Its approximate 300 species are common to soil, water, and decaying...
