Acremonium strictum

Acremonium strictum is an environmentally widespread saprotroph species found in soil, plant debris, and rotting mushrooms. Isolates have been collected in North and Central America, Asia, Europe and Egypt. A. strictum is an agent of hyalohyphomycosis and has been identified as an increasingly frequent human pathogen in immunosuppressed individuals, causing localized, disseminated and invasive infections. Although extremely rare, A. strictum can infect immunocompetent individuals, as well as neonates. Due to the growing number of infections caused by A. strictum in the past few years, the need for new medical techniques in the identification of the fungus as well as for the treatment of human infections has risen considerably. A. strictum has been shown to be involved in some myoparasitic relationships, as well as a wide range of plant endophytic and parasitic relationships, and further studies are required to determine A. strictum's use as a biological control agent and role as a parasite that reduces crop yields. A. strictum exhibits metabolism of many products that imply future agricultural and pharmaceutical significance. The genus Acremonium is a large polyphyletic genus of approximately 150 species, many of which are derived from a closely related families in the Sordariomycetes. The genus includes many slow growing, simply structured, anamorphic filamentous fungi, typically encountered in wet, cellulose-based building materials suffering form chronic wet conditions. Characteristic morphology in this genus is septate hyphae giving rise to thin, tapered aculeate phialides that are usually unicellular, or weakly branched conidiophores. Human infections, though rare, usually occur in severely immunodeficient individuals. A. strictum is mostly known to be involved with myparasitic relationships, as well as being a plant parasite and endophyte. Acremonium strictum grows readily at 30 °C on glucose peptone agar, showing mycelium of approximately 50mm in size in 7 days. Colonies are flat, with smooth, wet, velvety or floccose texture, sometimes resembling thin cottony mounds. The colour of mycelia ranges widely from light pink to orange, and sometimes yellow, white or green. A. strictum filaments are sometimes bound together into ropes several cells in diameter.Conidium grow as wet clusters or dry chains, and grains produced are white to pale-yellow, soft and variable in shape. Subcultures of the fungus can also be grow within seven days into smooth, moist, pink mycelia that resemble thin cotton. Under the microscope at 30 °C, A. strictum shows long slender phialides, and conidia are cylindrical or ellipsoidal, formed in slimy bundles at the tips of the phialides. Lower microscopy shows pin-head spore ball formation. Species of Acremonium are morphologically very similar, making identification difficult. Shown in the image is a microscopic image of A. falciforme, an example showing the morphological similarities to A. strictum. Cases involving different species of Acremonium are often reported as simply as an Acremonium species, which reduces the amount of accurate information on the clinical presentation of A. strictum. Isolates of phylogenetically remote species of Acremonium show considerable convergence. As a human pathogen, diagnosis is made in isolation and identification of the fungus from granules in tissue and the presence of hyphae in microscopic examination of cutaneous biopsy and discharge. Genera that are morphologically similar to Acremonium include Fusarium, Phaeoacremonium, Verticillium, Phialemonium, and Lecanicillium. Identification of A. strictum isolates has shown that this fungus is phenotypically diverse and may vary genetically. Due to phylogenetic ambiguities, an unknown proportion of the literature on A. strictum is based on studies of Acremonium sclerotigenum. The fungus can generally be successfully identified by the nuclear ITS region sequence analysis. Analysis of the genes for ribosomal large subunit (LSU) and whole small subunit (SSU) also help to elucidate phylogenetic relationships, since these genes are more conserved and less subject to evolutionary changes. The species A. strictum is separated into three genogroups. Genogroup I is represented by type strain CBS 346.70, genogroup II by UW836 and genogroup III by UWFP940. These genogroups were determined based on GenBank entries for A. strictum.