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ASPERGILLUS Mould
The
U.S. Government's
Occupational Safety and Health Administration [OSHA] lists
the following Aspergillus mould species as all being
allergens and irritants and a cause
of
Hypersensitivity pneumonitis and
Dermatitis : Aspergillus flavipes,
Aspergillus flavus,
Aspergillus fumigatus,
Aspergillus glaucus,
Aspergillus nidulans,
Aspergillus niger,
Aspergillus ochraceus,
Aspergillus versicolor. |
Taxonomic
Classifications
Kingdom: Fungi
Phylum: Ascomycota
Order: Eurotiales
Family: Trichocomaceae
Genus: Aspergillus
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Toxic Mould Species:
Mould Pictures Absidia Mould Alternaria Mould Aspergillus Mould Aureobasidium Mould Blastomyces Mould Candida Mould Coccidioides Cryptococcus Mould Curvularia Mould Histoplasma Mould Mucor Mould Penicillium Mould Pseudallescheria Sporothrix Mould Stachybotrys Mould Verticillium Mould Yeast |
 Recognized by its distinct conidiophores terminated by a swollen vesicle
bearing flask-shaped phialides. The phialides may be borne directly on
the vesicle (a) or on intervening metulae (b). Some species may form
masses of thick-walled cells called "hülle cells" (c). The spores come
in several colours, depending upon the species, and are produced in long
chains from the ends of the phialides. Commonly isolated from soil,
plant debris, and house dust; sometimes pathogenic to man. Holomorphs:
Emericella,
Eurotium,
Neosartorya, and others.
Refs: Raper and Fennell 1965; Samson 1979.
Source:
Mould Scientific Descriptions
by Prof. David. Malloch,
Department of Botany,
University of Toronto. |
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Source:
Mould
Help - Aspergillus
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Description and Habitats
Aspergillus mould is a filamentous, cosmopolitan and ubiquitous fungus
found in nature. It is commonly isolated from soil, plant debris, and
indoor air environment. While a teleomorphic state has been described only
for some of the Aspergillus spp., others are accepted to be
mitosporic, without any known sexual spore production.
Species
The genus Aspergillus includes over 185 species. Around 20 species
have so far been reported as causative agents of opportunistic infections in
man. Among these, Aspergillus fumigatus is the most commonly isolated
species, followed by Aspergillus flavus and Aspergillus niger.
Aspergillus clavatus, Aspergillus glaucus group,
Aspergillus nidulans, Aspergillus oryzae, Aspergillus terreus,
Aspergillus ustus, and Aspergillus versicolor are among the
other species less commonly isolated as opportunistic pathogens.
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Aspergillus flavus |
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Culture of Aspergillus flavus.
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Conidial head of
A. flavus.
Note: conidial heads with both uniseriate and biseriate arrangement of
phialides may be present.
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Clinical Significance of Aspergillus flavus
Aspergillus
flavus has a world-wide distribution and normally occurs as a
saprophyte in soil and on many kinds of decaying organic matter. A.
flavus is the second most common species (next to A. fumigatus)
to be isolated from human infections, and it is often associated with
invasive aspergillosis seen in immunosuppressed patients and in
paranasal sinus infections. |
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Source: Mycology Online (Mycology Online) |
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Aspergillus fumigatus |
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Culture of Aspergillus fumigatus
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Conidial head of
A. fumigatus
(Note: uniseriate row of phialides on
the upper two thirds of the vesicle)
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Clinical Significance of Aspergillus fumigatus
Based on the research
conducted by the National Center for
Biotechnology Information (NCBI), Aspergillus fumigatus
can also cause allergic bronchopulmonary and sinus infections. Patients
with asthma and cystic fibrosis can frequently develop allergic broncho-pulmonary
aspergillosis (ABPA), a hypersensitivity reaction to the fungus
Aspergillus fumigatus, which frequently leads to a progressive loss
in lung function. Morever, in developing countries patients with
compromised immune response can develop keratitis, which usually leads
to unilateral blindness.
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Source: Mycology Online
For more information on the different mould species, please
visit this website:
Mycology Online |
Health Effects
Aspergillus mould is prevalent
under a variety of moisture conditions as a contaminant on almost any
outdoor or indoor surface. There are at least 15 varieties of Aspergillus
mould that can be found in homes and offices, and most are allergy-inducing
or toxic. Aspergillus may produce volatile
organic compounds [VOCs] that result in unpleasant odors and cause Type I
and Type III allergies. It is implicated in numerous respiratory disorders
as well as infections of the ear, eye, and invasive diseases. Other
infection sites for susceptible individuals may vary widely.
Aspergillus may produce several
toxins with cytotoxic and carcinogenic [cancer-causing] effects. At least
four types of Aspergillus are toxigenic [poisonous]: (a) Aspergillus
parasiticus; (b) Aspergillus flavus; (c) Aspergillus versicolor; and (d)
Aspergillus fumigatus. These toxic Aspergillus varieties are known as
aflatoxins and are the most widely studied moulds in medical research. Aflatoxins are more toxic than many known industrial cancer causing
substances, they are acutely toxic to the liver, brain, kidneys, and heart,
and, with chronic exposure, are potent carcinogens of the liver. Symptoms of
acute aflatoxicosis are fever, vomiting, coma, and convulsions.
Aspergillus Niger has been
reported to cause skin and pulmonary infections. It is a common cause
of fungal related ear infections.
Other health effects of Aspergillus mould are---
Aspergillosis. Although metabolites of species of Aspergillus (Hyphomycetes)
cause other health problems, such as acute and chronic aflatoxin poisoning,
we are concerned here only with diseases caused by the growth of the fungus
itself somewhere in the body.
(1) Bronchopulmonary aspergillosis
is usually caused by Aspergillus fumigatus, which colonizes mucus
within the bronchi, evoking a severe allergic reaction.
(2) In Aspergilloma, the fungus
forms a mycelial ball in a lung cavity produced by an earlier attack of
tuberculosis. The wall of the cavity may erode, causing the patient to spit
blood, and necessitating surgical intervention.
(3) Invasive aspergillosis is found
only in patients who are severely debilitated, or are immunosuppressed, as
in AIDS. The fungus grows outward from the lung, invading blood vessels and
spreading to other organs through the bloodstream. This insidious disease is
usually fatal, and is often diagnosed only when an autopsy is performed.
[from Bryce Kendrick's The Fifth Kingdom]
Macroscopic
Features
The
major macroscopic features remarkable in species identification are the
growth rate, color of the colony, and thermotolerance.
Except for Aspergillus nidulans and Aspergillus glaucus, the
growth rate is rapid to moderately rapid. While Aspergillus nidulans
and Aspergillus glaucus grow slowly and reach a colony size of
0.5-1 cm following incubation at 25°C for 7 days on Czapek-Dox agar,
those of the remaining species are 1-9 cm in diameter in the specified
setting. These variations in growth rate help in species identification.
Aspergillus colonies are downy to powdery in texture. The surface
color may vary depending on the species. The reverse is uncolored to pale
yellow in most of the isolates. However, reverse color may be purple to
olive in some strains of Aspergillus nidulans and orange to purple
in Aspergillus versicolor (TABLE 1).
Aspergillus fumigatus is a thermotolerant fungus and grows well at
temperatures over 40°C. This property is unique to Aspergillus
fumigatus among the Aspergillus species. Aspergillus
fumigatus can grow at a temperature range of 20 to 50 °C.
The color of the
colony in various Aspergillus species.
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SPECIES
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SURFACE
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REVERSE
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A. clavatus
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Blue-green
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White, brownish with age
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A. flavus
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Yellow-green
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Goldish to red brown
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A. fumigatus
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Blue-green to gray
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White to tan
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A. glaucus group
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Green with yellow areas
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Yellowish to brown
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A. nidulans
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Green, buff to yellow
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Purplish red to olive
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A. niger
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Black
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White to yellow
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A. terreus
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Cinnamon to brown
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White to brown
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A. versicolor
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White at the beginning, turns to yellow, tan, pale green or pink
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White to yellow or purplish red
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Source of above
information: Doctor Fungus
Microscopic
Features
The basic microscopic morphology is same for all species. However, some
other microscopic structures are unique to certain species and constitute
the key features for species identification together with the surface
color of the colony (TABLE 2).
1. COMMON TO ALL SPECIES: Hyphae are septate and hyaline. The
conidiophores originate from the basal foot cell located on the supporting
hyphae and terminate in a vesicle at the apex. Vesicle is the typical
formation for the genus Aspergillus. The morphology and color of
the conidiophore vary from one species to another. Covering the surface of
the vesicle entirely ("radiate" head) or partially only at the
upper surface ("columnar" head) are the flask-shaped phialides
which are either uniseriate and attached to the vesicle directly or are
biseriate and attached to the vesicle via a supporting cell, metula. Over
the phialides are the round conidia (2-5 µm in diameter) forming radial
chains.
2. UNIQUE TO CERTAIN SPECIES ONLY: Other microscopic structures include
sclerotia, cleistothecia, aleuriconidia, and Hulle cells. These structures
are of key importance in identification of some Aspergillus
species. Cleistothecium is a round, closed structure enclosing the asci
which carry the ascospores. The asci are spread to the surrounding when
the cleistothecium bursts. Cleistothecium is produced during the sexual
reproduction stage of some Aspergillus species. Aleuriconidium is a
type of conidium produced by lysis of the cell that supports it. The base
is usually truncate and carries remnants of the lysed supporting cell.
These remnants form annular frills at its base. Hulle cell is a large
sterile cell bearing a small lumen. Similar to cleistothecium, it is
associated with the sexual stage of some Aspergillus species.
Microscopic features
of various Aspergillus species
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SPECIES
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CONIDIOPHORE
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PHIALIDES
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VESICLE
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S
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C
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HC
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A
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A. clavatus
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Long, smooth
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Uniseriate
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Huge, clavate-shaped
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-
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-
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-
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-
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A. flavus
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Colorless, rough
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Uni-/biseriate
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Round, radiate head
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+ (In some strains, brown)
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-
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-
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-
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A. fumigatus
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Short (<300 µm), smooth, colorless or greenish
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Uniseriate
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Round, columnar head
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-
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-
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-
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-
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A. glaucus group
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Variable length, smooth, colorless
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Uniseriate
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Round, radiate to very loosely columnar head
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-
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+ (yellow -orange)
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-
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-
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A. nidulans
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Short (<250 µm), smooth, brown
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Biseriate, short
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Round, columnar head
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-
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+ (red)
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+
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-
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A. niger
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Long, smooth, colorless or brown
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Biseriate
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Round, radiate head
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-
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-
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-
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-
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A. terreus
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Short (<250 µm), smooth, colorless
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Biseriate
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Round, compactly columnar head
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-
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-
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-
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+ (solitary, round, produced directly on hyphae)
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A. versicolor
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Long, smooth, colorless
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Biseriate
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Round, loosely radiate head
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-
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-
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+ (in some strains)
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-
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S:
Sclerotia
C: Cleistothecia
HC: Hulle cells
A: Aleuriconidia
Source of above information : Doctor Fungus
Laboratory
Precautions
No special precautions other than general
laboratory precautions are required.
Susceptibility
Following the documentation
of the NCCLS proposed standard (M38-P) for in vitro susceptibility testing
of filamentous fungi, more data have been available on in vitro activity
of Aspergillus spp. Although the MIC breakpoints for the available
antifungal agents are not defined yet, the results of these studies are in
consensus for a number of features. The MICs obtained for different
species of Aspergillus are in general similar. While most of the Aspergillus
isolates yield acceptably low MICs for
amphotericin
B,
itraconazole,
and
voriconazole,
high MICs potentially predictive of resistance have been reported for a
number of isolates. Among these are, amphotericin B MICs for Aspergillus
terreus. A few itraconazole-resistant Aspergillus fumigatus
isolates have also been identified. Significantly and finally,
voriconazole appears effective in vitro against itraconazole-resistant Aspergillus
fumigatus.
The in vitro activity of novel antifungal agents, such as the
echinocandins
are also of current interest. Although the visualization of the in vitro
effect of echinocandins requires distinctive parameters (MEC; minimum
effective concentration), they are active against Aspergillus both
in vitro and in vivo. The recent demonstration of the synergistic effect
of amphotericin B with echinocandins against Aspergillus in vitro
and in animal models is noteworthy and exciting. (Arikan, ICAAC 2000).
Correlation of the in vitro susceptibility test results with the clinical
outcome has been documented for itraconazole and Aspergillus.
Treatment of invasive aspergillosis is still troublesome with high rate of
mortality. While amphotericin B (including its lipid formulations) and
itraconazole are the currently available therapeutic options, the clinical
success rate is still unsatisfactory due both to the low efficacy and/or
high toxicity of the drugs and existence of unfavorable immune status of
the host, such as lack of recovery from neutropenic state. The
concommitant use of colony stimulating factors may activate the
macrophages, enhance their fungicidal activity and prevent dissemination
of the infection.
The novel
azoles
(e.g., voriconazole, posaconazole, or ravuconazole),
glucan
synthesis inhibitors (e.g., caspofungin, V-echinocandin, FK463) and
liposomal
nystatin are active in vitro against Aspergillus and remain
promising for future therapy of aspergillosis.
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