Zygomycetes in Human Disease

Abstract

SUMMARY The Zygomycetes represent relatively uncommon isolates in the clinical laboratory, reflecting either environmental contaminants or, less commonly, a clinical disease called zygomycosis. There are two orders of Zygomycetes containing organisms that cause human disease, the Mucorales and the Entomophthorales. The majority of human illness is caused by the Mucorales. While disease is most commonly linked to Rhizopus spp., other organisms are also associated with human infection, including Mucor, Rhizomucor, Absidia, Apophysomyces, Saksenaea, Cunninghamella, Cokeromyces, and Syncephalastrum spp. Although Mortierella spp. do cause disease in animals, there is no longer sufficient evidence to suggest that they are true human pathogens. The spores from these molds are transmitted by inhalation, via a variety of percutaneous routes, or by ingestion of spores. Human zygomycosis caused by the Mucorales generally occurs in immunocompromised hosts as opportunistic infections. Host risk factors include diabetes mellitus, neutropenia, sustained immunosuppressive therapy, chronic prednisone use, iron chelation therapy, broad-spectrum antibiotic use, severe malnutrition, and primary breakdown in the integrity of the cutaneous barrier such as trauma, surgical wounds, needle sticks, or burns. Zygomycosis occurs only rarely in immunocompetent hosts. The disease manifestations reflect the mode of transmission, with rhinocerebral and pulmonary diseases being the most common manifestations. Cutaneous, gastrointestinal, and allergic diseases are also seen. The Mucorales are associated with angioinvasive disease, often leading to thrombosis, infarction of involved tissues, and tissue destruction mediated by a number of fungal proteases, lipases, and mycotoxins. If the diagnosis is not made early, dissemination often occurs. Therapy, if it is to be effective, must be started early and requires combinations of antifungal drugs, surgical intervention, and reversal of the underlying risk factors. The Entomophthorales are closely related to the Mucorales on the basis of sexual growth by production of zygospores and by the production of coenocytic hyphae. Despite these similarities, the Entomophthorales and Mucorales have dramatically different gross morphologies, asexual reproductive characteristics, and disease manifestations. In comparison to the floccose aerial mycelium of the Mucorales, the Entomophthorales produce a compact, glabrous mycelium. The asexually produced spores of the Entomophthorales may be passively released or actively expelled into the environment. Human disease with these organisms occurs predominantly in tropical regions, with transmission occurring by implantation of spores via minor trauma such as insect bites or by inhalation of spores into the sinuses. Conidiobolus typically infects mucocutaneous sites to produce sinusitis disease, while Basidiobolus infections occur as subcutaneous mycosis of the trunk and extremities. The Entomophthorales are true pathogens, infecting primarily immunocompetent hosts. They generally do not invade blood vessels and rarely disseminate. Occasional cases of disseminated and angioinvasive disease have recently been described, primarily in immunocompromised patients, suggesting a possible emerging role for this organism as an opportunist.

Fungi associated with the traditional starter cultures used for rice wine in Korea

“…Aspergillus isolates were grown for 7 days on Czapek yeast agar (CYA) at either 25 or 37 o C, CYA with 20% sucrose (CY20S) at 25 o C or MEA at 25 o C. For micromorphological observations, the fruiting bodies of fungi were observed with a SMZ1500 stereoscopic microscope (Nikon, Tokyo, Japan), and the vegetative and asexual stages were observed with a DE/Axio Imager A1 microscope (Carl Zeiss, Oberkochen, Germany) after staining MEA colonies with lactophenol cotton blue (BD Biosciences). The morphological features of the isolates were characterized, and the species were identified according to the methods of previous studies on Mucorales [Ciesla et al, 2000;Ribes et al, 2000;Garcia-Hermoso et al, 2009] and of Aspergilli [Klich, 2002]. All Aspergillus isolates thought to be of the Aspergillus section Flavi were cultured on Aspergillus flavus and Aspergillus parasiticus agar (AFPA) (Oxoid, Cambridge, UK) for 3-5 days at 25 o C in the dark, and the colony color was then observed as previously described [Rodrigues et al, 2009].…”

“…A member of Mucorales, Rhizopus, also has been frequently used to investigate the development of new types of modified Nuruk [Lee et al, 1987;Shon et al, 1990;So, 1995;Lee et al, 2002;Yu et al, 2002]. Members of the order Mucorales are widely distributed in food, soil, and air [Guarro et al, 1999;Ribes et al, 2000]. Aspergilli, belonging to the order Eurotiales, are globally the most abundant and widely distributed organisms [Klich, 2002].…”

Infectious Agents

“…The hyphae of the Zygomycetes are relatively broad (5-20 μm), thin-walled and coenocytic (aseptate). 18 Budding yeasts with narrow bases and broad pseudohyphae having constricted septa can indicate pathogenic Candida species. 19 The dematiaceous fungi causing abortions have brown to black intracellular pigment (melanin) that is easily seen.…”

Zygomykosen nach Blutstammzelltransplantation—ein aktuelles Problem?

“…Die definitive Diagnose einer Zygomykose erfordert den histopathologischen Nachweis der Myzelien in Biopsiematerial [25]. Typisch sind unseptierte, mehrkernige Hyphen, wobei die Unterscheidung von Aspergillus spp.…”

“…schwierig sein kann. Für die Kultur von Zygomykosen fehlen standardisierte Protokolle; sie wird vor allem durch die mechanische Empfindlichkeit der Hyphen erschwert [25]. In einer großen Fallserie waren 75% der Kulturen von Patienten mit histopathologisch dokumentierter Zygomykose negativ [13].…”