Submitted to: Medical Mycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2006
Publication Date: 9/1/2006
Citation: Klich, M.A. 2006. Identification of clinically relevant Aspergilli. Medical Mycology. 44:5127-5131.
Interpretive Summary: When people’s immune systems are damaged, either through disease (such as AIDS or diabetes) or intentionally (for transplant patients), they become susceptible to fungal infections. Infections from the fungus Aspergillus are increasing as the immunosuppressed portion of our population increases. Aspergillus also causes allergies and produces toxins that can damage organs or kill people. Identification of these fungi is critical in determining appropriate treatment, studying epidemiology, disease prognosis and litigation pertaining to the disease. In this paper, I have critically reviewed the strengths and weaknesses of the various methods of identification; summarized the identification systems (keys) currently available; and given advice on the kinds of identification keys that are best suited for various purposes. This article is meant for clinicians and those needing to select the appropriate identification system for their purposes.
Technical Abstract: Historically, classification and identification of aspergilli was accomplished using morphological characteristics. A number of molecular, immunological and biochemical methods are now available. Some of these methods are designed to identify only a few species, whereas others address most of the important species in the genus. For the most part, the results of the various approaches concur, yielding similar results in identifying aspergilli. The identification method used should be a function of the needs of the clinician or researcher. In most clinical settings, immediate identification of the species causing a fungal disease is less important than rapid determination of the treatment regime that will be most efficacious for the patient. This may not require identification of the isolate to the species level. Speciation and ‘fingerprinting’ of strains become important in determining etiology and epidemiology of the disease. In these situations, accuracy of the identification is more important than the speed at which the identification is performed. In such cases, researchers frequently use more than one method of identification. The number of species reported to cause aspergillosis is growing, therefore, any accurate system of identification of clinical isolates must include species not yet reported in clinical cases. Each identification method has advantages and disadvantages. The morphological approach is the least expensive and quite accurate, but it requires use of a standardized plating and incubation regime, some skill with a microscope and an understanding of the characteristics of the genus. Like the morphological approach, the biochemical approach requires culturing the fungi, but is a bit limited because not all isolates of a species consistently produce the same metabolites. Although inexpensive, use of thin layer chromatography plates can yield good information for identification, but metabolites can only be accurately identified with more sophisticated equipment for HPLC and mass spectroscopy. Immunological methods may be used on tissue samples, but are currently limited because they have been developed for only a few taxa. Molecular methods have the advantage of not necessarily requiring isolation or culturing of the fungi and require only a skilled technician for acquiring data, however, the equipment necessary for molecular work is very expensive, accepted molecular methodologies change frequently, and the process needs to be overseen by a well-trained molecular biologist to avoid potential errors in identification.