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Acremonium Species

The U.S. Government's Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Acremonium mold: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis.

Taxonomic Classification

Kingdom: Fungi
Phylum: Ascomycota
Subphylum: Ascomycotina
Order: Hypocreales
Family: Hypocreaceae
Genus: Acremonium


 

Acremonium species showing long awl-shaped phialides producing cylindrical,
one-celled conidia mostly aggregated in slimy heads at the apex of each phialide.

Colonies are usually slow growing, often compact and moist at first, becoming powdery, suede-like or floccose with age, and may be white, grey, pink, rose or orange in color. Hyphae are fine and hyaline and produce mostly simple awl-shaped erect phialides. Conidia are usually one-celled (ameroconidia), hyaline or pigmented, globose to cylindrical, and mostly aggregated in slimy heads at the apex of each phialide.

This genus is distinguished from hyaline isolates of Phialophora by the absence or very limited development of a collarette on the phialide and the predominant formation of well differentiated, awl-shaped phialides with a basal septum. Microconidial Fusarium isolates may be confused with Acremonium, but they usually grow faster and have colonies with a characteristic fluffy appearance.

        For identification, potato dextrose agar and cornmeal agar are the most suitable media to use and exposure to daylight is recommended to maximize culture color characteristics.

Description and Natural Habitats

Acremonium species. 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.

According to The Environmental Reporter, Vol. 3, No. 9, “Acremonium species is primarily isolated from soil, plant debris, foodstuffs, hay, rotting mushrooms, and indoor building materials, such as the acoustic and thermal fiber glass insulation used in heating ventilation and air conditioning system.  Acremonium has a high water affinity of Aw 0.90-0.98 and is often isolated from cooling coils, drain pans, window seals, and water from humidifiers.  Additionally, Acremonium is occasionally found growing with Stachybotrys.  The spores of this fungus are formed in a slimy mass resulting to a limited aerosolization.”

 

Species

The genus Acremonium currently contains 100 species, of which most are saprophytic, being isolated from dead plant material and soil. There are three main species of Acremonium implicated in infections: Acremonium falciforme, Acremonium kiliense, and Acremonium recifei.
 

Pathogenicity  and Clinical Significance

Acremonium is considered as one of the causative agents of white grain mycetoma.  In addition to some cases of onychomycosis due to Acremonium, cases of endocarditis, endophthalmitis, keratitis, meningitis, and peritonitis have also been reported.  This fungus is known to cause opportunistic infections mainly among the immunocompromised patients, such as bone marrow transplant recipients. 

 

Acremonium species are encountered as contaminants as well thus; their isolation in culture requires careful evaluation.  Additionally, some Acremonium species are even parasitic toward other fungal organisms which are generally termed as mycoparasites.

 

Macroscopic Features

     Growth rate is moderately rapid and colonies are compact, flat or folded and occasionally raised in the center; initially, texture is glabrous, velvety and membrane – like and becoming cottony with age due to the overgrowth of loose hyphae;

     Colonies are observed having diameter measuring from 1 to 3 cm after seven days of incubation at 25ฐC; and

     Surface colony color ranges from white, to pale gray or pale pink while the reverse is uncolored or a pink to rose colored - pigmentation may be observed.

 

Microscopic Features

      Hyphae are hyaline and septate which are characteristically fine and narrow;

      Phialides are erect, unbranched and solitary which arise directly from the hyphal tips; phialides are separated by a septum from the hyphae and taper towards their tips; and

      Conidia are hyaline, may be unicellular or multicellular, fusiform – shaped with a slight curve or may look like a shallow crescent, appear in clusters, in balls or as fragile chains rarely, with size of 2 – 3 x 4 – 8 ตm, and are found at the tips of the phialides; the structural properties of the conidia may vary depending on the species.

 

           Table 1.  Structural Differences of Conidia of Acremonium species

Acremonium species

Structural Differences of Conidia

Acremonium falciforme

Produces crescent - shaped, non -septate conidia, 2 - or 3 - celled conidia may also be observed sometimes

Acremonium kiliense

Produces short straight conidia

Acremonium recifei

Produces usually crescent – shaped  and non – septate conidia

 

“The wet conidial spores are disseminated mechanically by insects or water droplets.  Occasionally, spores from old growth are wind disseminated,” according to The Environmental Reporter, Vol. 3, No. 9

 

Mold Analysis

On spore traps, Acremonium is not easily identified due to their very small, colorless and non – distinctive spores.  Furthermore, some spores are so small that they may be obscured by background debris.  Air sampling cultures are a better way to recover and identify airborne Acremonium spores.   Acremonium can easily be identified on direct examination as it is possible to view distinctive chains or the slimy heads of conidia.

Laboratory Precautions

Since Acremonium species are cosmopolitan nature, they are also encountered as contaminants. Thus isolation in culture requires cautious evaluation.

 

Susceptibility
 

Reported data on in vitro susceptibility are very limited.  The novel azoles, posaconazole and voriconazole show favorable in vitro activity against Acremonium strains. 

 

On the other hand, in vivo response largely depends on both antifungal therapy and surgical involvement.  Amphotericin B remains as the mainstay of therapy among the available antifungal agents.

The mycological information gathered and organized in this extensive research on different Pathogenic Molds was  sourced out from the list of informative websites below:

  http://www.osha.gov | http://www.doctorfungus.org | http://www.mycology.adelaide.edu.au | http://www.mycology.net | http://www.dehs.umn.edu | http://www.mold-help.org |http://www.mycology.net | http://www.pfdb.net | http://www.clinical-mycology.com | http://www.botany.utoronto.ca | http://www.med.sc.edu | http://www.tigr.org | http://www.pangloss.ucsfmedicalcenter.org | http://www.dermnz.org | http://ncbi.nlm.nih.gov | http://www.wadsworth.org | http://botit.botany.wisc.edu

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