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Absidia species are
filamentous fungi that are cosmopolitan and ubiquitous in nature as common
environmental contaminants. They are usually found in food, plant debris
and soil, as well as being isolated from foods and indoor air environment.
They often cause food spoilage like on decaying vegetables in the
refrigerator and on moldy bread.
The genus Absidia currently
contains 21 species. The most commonly isolated species is Absidia
corymbifera. It is the only recognized pathogen among the other Absidia
species. Some of the other Absidia species are Absidia coerulea,
Absidia cylindrospora, Absidia glauca, and Absidia
spinosa.
According
to the study of Microbiology and Immunology On-line, the Absidia species
is one of the three most common genera that can cause ZYGOMYCOSIS which
also known as mucormycosis and phycomycosis. Zygomycosis is an acute
inflammation of soft tissue, usually with fungal invasion of the blood
vessels. This rapidly fatal disease is caused by several different species
in this class. The zygomycetes, like the Candida species, are ubiquitous
and rarely cause disease in an immunocompetent host. Some characteristic
underlying conditions which cause susceptibility are: diabetes, severe
burns, immunosuppression or intravenous drug use.
These fungi have a tendency to invade blood vessels (particularly
arteries) and enter the brain via the blood vessels and by direct
extension through the cribiform plate. Rhinocerebral infections are
usually fulminant and frequently fatal. This is why they cause death so
quickly. Macroscopic Features
Absidia
corymbifera
grows rapidly. The rapid growing, flat, woolly to cottony, and olive gray
colonies mature within 4 days. The diameter of the colony is 3-9 cm
following incubation at 25°C for 7 days on potato glucose agar. The
texture of the colony is typically woolly to cottony. From the surface,
the colony is grey in color. The reverse side is uncolored and there is no
pigment production. Absidia corymbifera is a
psychrotolerant-thermophilic fungus. It grows more rapidly at 37°C than
at 25°C. Its maximum growth temperature is as high as 48 to 52°C. The
growth of Absidia corymbifera is optimum at 35-37°C and at a pH
value of 3.0 to 8.0. Microscopic Features
Similar
to that of the other members of the class Zygomycetes,
Absidia corymbifera has wide (6-15 µm in diameter) nonseptate
hyphae. A few septa may occasionally be present. Rhizoids are rarely
observed. When present, the sporangiophores arise on stolons from points
between the rhizoids, but not opposite the rhizoids. The sporangiophores
are branched and arise in groups of 2-5 at the internodes. They often
produce arches. Sporangiophores carry pyriform, relatively small (20-120
µm in diameter) sporangia. A septum is usually present just below the
sporangium in the sporangiophore. The sporangiophore widens to produce the
funnel-shaped apophysis beneath the sporangium. The apophysis of Absidia
corymbifera is very well-developed and typical. The columella, the tip
of the sporangiophore that extends into the sporangium, is semicircular in
shape and has a small projection on top. Upon dissolving of the sporangial
wall, a short remaining collarette may be observed overlining the
apophysis. The sporangiospores are one-celled, hyaline to light black,
round to oval in shape, smooth or rarely echinulate on surface and 3-4.5
µm in diameter. They are found in the sporangium and are released to the
surrounding when the sporangium ruptures.
No special precautions other than general laboratory precautions are
required.
Susceptibility
In vitro susceptibility data reported so far are limited . MIC breakpoints
for interpretation of in vitro susceptibility results have not been
defined. Similar to the other members of the class Zygomycetes, amphotericin
b appears as the sole antifungal drug which is consistently active
against Absidia corymbifera . In general, it is resistant to azoles,
including the newer derivatives such as voriconazole. flucytosine
is also ineffective against Absidia corymbifera . Some strains may
yield relatively low MICs of sordarin group of compounds. However, the
significance of this finding is unclear. In vivo response, on the other hand, largely depends on administration of full-dose amphotericin B therapy as well as extensive surgical debridement and correction of the underlying predisposing factors (such as immunosuppression and diabetic acidosis). The mycological information gathered and organized in this extensive research on different Pathogenic Molds was sourced out from the list of informative websites below:
1. http://www.osha.gov
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