Acremonium spp.

Abstract

Taxonomic Classification Kingdom: Fungi Phylum: Ascomycota Subphylum: Ascomycotina Order: Hypocreales Family: Hypocreaceae Genus: Acremonium Description and Natural Habitats Acremonium spp. are filamentous, cosmopolitan fungi commonly isolated from plant debris and soil. The sexual state of Acremonium is not well-defined. Thus, it is classified among the deuteromycetes group of fungi by some authorities. Others prefer to include it in Ascomycota phylum, due to its structural properties similar to those of this group. Species There are three main species of Acremonium implicated in infections: Acremonium falciforme, Acremonium kiliense, and Acremonium recifei. See the list of obsolete names and synonyms for older names of these species. Pathogenicity and Clinical Significance Acremonium is one of the causative agents of eumycotic white grain mycetoma. Rare cases of onychomycosis, keratitis, endophthalmitis, endocarditis, meningitis, peritonitis, and osteomyelitis due to Acremonium have also been reported [730, 952]. This fungus is known to cause opportunistic infections in immunocompromised patients, such as bone marrow transplant recipients [1581]. Infections of artificial implants due to Acremonium spp. are occasionally observed [1750]. Since Acremonium species are cosmopolitan in nature, they are also encountered as contaminants. Thus, their isolation in culture requires cautious evaluation. Macroscopic Features The growth rate of Acremonium colonies is moderately rapid, maturing within 5 days. The diameter of the colony is 1-3 cm following incubation at 25°C for 7 days on potato glucose agar. The texture of the colony is compact, flat or folded, and occasionally raised in the center. It is glabrous, velvety, and membrane-like at the beginning. Powdery texture may also be observed. By aging, the surface of the colony may become cottony due to the overgrowth of loose hyphae. The color of the colony is white, pale grey or pale pink on the surface. The reverse side is either uncolored or a pink to rose colored pigment production is observed [462, 1295, 2144]. Microscopic Features Acremonium spp. possess hyaline, septate hyphae which are typically very fine and narrow. Vegetative hyphae often form hyphal ropes. Unbranched, solitary, erect phialides are formed directly on the hyphal tips, the hyphal ropes, or both. The phialides are separated from hyphae by a septum and taper towards their apices. At the apices of the phialides are the hyaline conidia 2-3x4-8μm in size. They usually appear in clusters, inballs or rarely as fragile chains. The conidia are bound by a gelatinous material. They maybe single or multicellular, fusiform with a slight curve or resemble a shallow crescent.These structural properties of conidia vary depending on the species. Acremoniumfalciforme usually produces crescentic, nonseptate conidia. Sometimes, 2- or 3-celledconidia may also be observed. Acremonium kiliense, on the other hand, has short straightconidia and the conidia of Acremonium recifei are usually crescentic and nonseptate [462,1295, 2144]. Histopathologic Features The grains (500-2000μm in size) of Acremonium spp. are regular and oval to round inshape. When stained with H&E, poorly staining dense hyphal packs are observed [462]. Compare to Ascocoryne, Fusarium, Lecythophora, Phialemonium, Phialoacremonium, Sporothrix, andVerticillium. Key Features for Differentiation Laboratory Precautions No special precautions other than general laboratory precautions are required. Susceptibility In vitro susceptibility data reported so far are limited. MIC breakpoints for interpretation ofin vitro susceptibility results have not been defined. Recent work has focused ondetermination of the efficacy of novel antifungal agents against Acremonium. The novelazoles, such as voriconazole, and posaconazole appear to exhibit favorable in vitro activityagainst Acremonium strains. Itraconazole MICs obtained forAcremonium isolates, on theother hand, are somewhat higher than those of voriconazole. Among the glucan synthesisinhibitors, the MICs of caspofungin are lower than those of V-echinocandin [683, 914, 1434, 1494]. In vivo response, on the other hand, depends on both antifungal therapy and surgicalintervention. Among the available antifungal agents, amphotericin B remains as themainstay of therapy. Acremonium spp. may also respond to azoles, which are occasionallyused in combination with amphotericin B. The limited data obtained so far for voriconazoleappear promising [730].