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Description and Natural Habitats Specimens of Alternaria are often found growing on carpets, textiles and horizontal surfaces such as window frames. It is commonly found in soil, seeds and plants. It is known to be a common allergen. It appears as a velvety tuft with long soft hairs and its color ranges from dark olive green to brown. Alternaria is a dry spore and is readily found in air samples as well as on tape lift samples. Alternaria is commonly found in water damaged buildings, and a significant increase in its numbers compared to outdoor levels can be a sign of growth. Commonly found in outdoor air, on many kinds of plants and food products and prefers rotting farmland manure. It may be resistant to fungicides. Alternaria is considered an occasional contaminant of water damaged building materials which contain cellulose. Although Alternaria is a notable source of fungal allergy, pathogenic infections are also reported infrequently. Species The genus Alternaria currently contains around 50 species. Among these, Alternaria alternata is the most common one isolated from human infections. Some authorities suggest that Alternaria alternata is a representative species complex rather than a single species and consists of several heterogenous species. While Alternaria chartarum, Alternaria dianthicola, Alternaria geophilia, Alternaria infectoria, Alternaria stemphyloides, and Alternaria teunissima are among the other Alternaria spp. isolated from infections, some Alternaria strains reported as causative agents remain unspecified. |
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Health Effects Among the species of alternaria, the
species Alternaria alternata is capable of producing tenuazonic acid and
other toxic metabolites which may be associated with disease in humans or
animals. Alternaria produces large spores having sizes between 20 - 200
microns in length and 7 - 18 microns in width, suggesing that the spores
from this fungi are deposited in the nose, mouth, and upper respiratory
tract. It may be related to bakers asthma. It has been associated with
hypersensitivity pneumonitis, sinusitis, deratomycosis, onychomycosis,
subcutaneous phaeohyphomycosis, and invasive infection. Common cause of
extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms
include edema and bronchiospasms, chronic cases may develop pulmonary
emphysema. Further explanations about the health disease caused by
alternaria species shown below:
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Macroscopic
Features Alternaria
spp. grow rapidly and the colony size reaches a diameter of 3 to 9 cm
following incubation at 25°C for 7 days on potato glucose agar. The
colony is flat, downy to woolly and is covered by grayish, short, aerial
hyphae in time. The surface is greyish white at the beginning which later
darkens and becomes greenish black or olive brown with a light border. The
reverse side is typically brown to black due to pigment production.
Microscopic
Features Alternaria
spp. have septate, brown hyphae. Conidiophores are also septate and brown
in color, occasionally producing a zigzag appearance. They bear simple or
branched large conidia (7-10 x 23-34 µm) which have both transverse and
longitudinal septations. These conidia may be observed singly or in
acropetal chains and may produce germ tubes. They are ovoid to obclavate,
darkly pigmented, muriform, smooth or roughened. The end of the conidium
nearest the conidiophore is round while it tapers towards the apex. This
gives the typical beak or club-like appearance of the conidia Laboratory
Precautions
No special precautions other than general laboratory precautions are
required. Susceptibility
In vitro susceptibility
testing for phaeoid fungi is not standardized yet. The in vitro activity
of some novel antifungal drugs has so far been investigated. While caspofungin
was shown to be active in vitro against Alternaria,
voriconazole
also appeared promising and generated lower MICs than itraconazole
for Alternaria strains . |
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The mycological information gathered and organized in
this extensive research on the different Pathogenic Molds was sourced
out from the list of websites below: |
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Browse these Webpages
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