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Mucor dimorphism has interested microbiologists since the time of Pasteur. When deprived of oxygen, these fungi grow as spherical, multipolar budding yeasts. In the presence of oxygen, they propagate as branching coenocytic hyphae. The ease with which these morphologies can be manipulated in the laboratory, the diverse array of morphopoietic agents available, and the alternative developmental fates that can be elicited from a single cell type (the sporangiospore) make Mucor spp. a highly propitious system in which to study eukaryotic cellular morphogenesis. The composition and organization of the cell wall differ greatly in Mucor yeasts and hyphae. The deposition of new wall polymers is isodiametric in yeasts and apically polarized in hyphae. Current research has focused on the identity and control of enzymes participating in wall synthesis. An understanding of how the chitosome interacts with appropriate effectors, specific enzymes, and the plasma membrane to assemble chitin-chitosan microfibrils and to deposit them at the proper sites on the cell exterior will be critical to elucidating dimorphism. Several biochemical and physiological parameters have been reported to fluctuate in a manner that correlates with Mucor morphogenesis. The literature describing these has been reviewed critically with the intent of distinguishing between causal and casual connections. The advancement of molecular genetics has afforded powerful new tools that researchers have begun to exploit in the study of Mucor dimorphism. Several genes, some encoding products known to correlate with development in Mucor spp. or other fungi, have been cloned, sequenced, and examined for transcriptional activity during morphogenesis. Most have appeared in multiple copies displaying independent transcriptional control. Selective translation of stored mRNA molecules occurs during sporangiospore germination. Many other correlates of Mucor morphogenesis, presently described but not yet explained, should prove amenable to analysis by the emerging molecular technology.
Mucor dimorphism has interested microbiologists since the time of Pasteur. When deprived of oxygen, these fungi grow as spherical, multipolar budding yeasts. In the presence of oxygen, they propagate as branching coenocytic hyphae. The ease with which these morphologies can be manipulated in the laboratory, the diverse array of morphopoietic agents available, and the alternative developmental fates that can be elicited from a single cell type (the sporangiospore) make Mucor spp. a highly propitious system in which to study eukaryotic cellular morphogenesis. The composition and organization of the cell wall differ greatly in Mucor yeasts and hyphae. The deposition of new wall polymers is isodiametric in yeasts and apically polarized in hyphae. Current research has focused on the identity and control of enzymes participating in wall synthesis. An understanding of how the chitosome interacts with appropriate effectors, specific enzymes, and the plasma membrane to assemble chitin-chitosan microfibrils and to deposit them at the proper sites on the cell exterior will be critical to elucidating dimorphism. Several biochemical and physiological parameters have been reported to fluctuate in a manner that correlates with Mucor morphogenesis. The literature describing these has been reviewed critically with the intent of distinguishing between causal and casual connections. The advancement of molecular genetics has afforded powerful new tools that researchers have begun to exploit in the study of Mucor dimorphism. Several genes, some encoding products known to correlate with development in Mucor spp. or other fungi, have been cloned, sequenced, and examined for transcriptional activity during morphogenesis. Most have appeared in multiple copies displaying independent transcriptional control. Selective translation of stored mRNA molecules occurs during sporangiospore germination. Many other correlates of Mucor morphogenesis, presently described but not yet explained, should prove amenable to analysis by the emerging molecular technology.
SUMMARYThe Authors present a case of subcutaneous mucormycosis occurring in a patient with clinical and biochemical evidence of diabetic ketoacidosis. The clinical, mycological and histopathological features are described, emphasizing the relevance of a rapid diagnosis in order to stablish early treatment. The clinical forms of mucormycosis and the main associated conditions are briefly reviewed as well as the most probable conditions which may lead to the enhanced susceptibility to infection in the diabetic patient in ketoacidosis. The recovery of Rhizo¬ pus oryzae from the air of the room of the patient suggests a nosocomial infection acquired through contamination of venous puncture site by air borne spores. INTRODUCTIONThe human infections caused by fungi of the class Zygomycetes are cosmopolitan and have been reported in normal and immunocompromised hosts. The disease has been generically called Zygomycosis (Phycomycosis). GREER 12 suggested the terms Mucormycosis and Entomophtoromycosis to name the infections restrictly caused by Zygomycetes of the orders Mucorales and Entomophtorales, since they are different diseases 12 . The human mucormycosis is world-wide in distribution often as an opportunistic infection and rarely affecting immunologicaly normal individuals 18 . Frequently it is a disease of acute evolution, characterized by invasion and growth of Mucorales in the vascular wall and lumen, with subsequent mycotic thromboembolism, ischemia, tissue necrosis and eventually death depending on the effected site. The rhinocerebral variant is the most acute and fulminant of the known mycosis 21 .22. The entomophtoromycosis, also known as subcutaneous zygomycosis or basidiobolomycosis is restricted to tropical and subtropical regions, being reported the cases mainly from Africa and Asia, and occasionally from South America 5 . 13 . 18 . Generally it has a chronic evolution characterized by the development of eosinophilic granuloma in the subcutaneous fat, rhino-orbital cavities and other areas of the organism, with swelling of the affected regions. The patients are apparently healthy 6 . 18 . 19 .The agents of mucormycosis are ubiquitous in nature, where they live on decaying organic material as saprophytes. They may be isolated from the air, soil, fruits, clinical materials and human orifices 4 . They reproduce by sexual and asexual ways and in the anamorphic (asexual) state form a great amount of spores inside sacular structures called sporangia. The principal way of dissemination is the air. The primary or exogenous cutaneous and subcutaneous mucormycosis is a rare occurrence and the way of infection is related to the rupture of the skin barrier with subsequent development of necrotic lesions in the skin or subcutaneous iat i5 . 2i .Recently microepidemics of cutaneous mucormycosis were reported in hospitals and were related to the use of elasticized adhesive tape dressings on open wounds in immunocompromised patients 1U3 as well in patients with orthopedic problems and whithout apparent immunological c...
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