Description and Habitats
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
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.
Another common health effect of Absidia species, is Rhinocerebral
infections. This disease is frequently seen in the uncontrolled
TYPICAL CASE: An uncontrolled diabetic patient comes to ER (may be comatose
depending on the state of diabetes) and a cotton-like growth is observed on
the roof of the mouth or in the nose. These are the hyphae of the organism.
If untreated, the patient will die within a few hours or days. What do you
do to help this patient first? Controlling the diabetic state is most
important before administering amphotericin.
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.
Absidia species may also cause mucorosis
in immune compromised individuals. Mucurosis
is an infection with tissue invasion by broad, nonseptate, irregularly
shaped hyphae of diverse fungal species such as Absedia species.
The sites of infection are the lung, nasal sinus, brain, skin and eye (Mycotic
Keratitis-infection of cornea which can
lead to blindness). Infection may have multiple sites. One species of
Absidia which is the Absidia cormbifera has been an invasive
infection agent in AIDS and neutropenic patients, as well as, agents of
bovine mycotic abortions, and feline subcutaneous abscesses.
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.
Similar to that of the other members of the class
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
precautions are required, no special safety measures needed.
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
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).
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