Absidia

The U.S. Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Absidia mould fungus:  Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis.

Species

The genus Absidia currently contains 21 species. The most commonly isolated species is Absidia corymbifera and it is the only recognized pathogen among the Absidia species. Other common Absidia species are Absidia coerulea, Absidia cylindrospora, Absidia glauca, and Absidia spinosa.

Taxonomic Classification

     Kingdom: Fungi
     Phylum : Zygomycota
     Subphylum : Zygomycotina
     Class : Zygomycetes
     Order : Mucorales
     Family : Mucoraceae
     Genus : Absidia
 

Absidia corymbifera colonies mature rapidly and resemble coarse, gray wool or cotton candy. The underside is uncolored and there is no pigment production.

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

Description and Habitat

Absidia moulds are filamentous fungi that are very 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, decaying vegetables in the refrigerator and are present on mouldy bread.

Absidia corymbifera grows rapidly. The rapid growing colonies are flat, woolly to cottony, and coloured olive gray. The texture of the colony is typically woolly to cottony. From the surface, the colony is grey in color. The underside is uncolored and there is no pigment production.

The colonies mature rapidly and become reproductive in 4 days.  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. Absidia corymbifera grows best at 35-37°C and at a pH value of 3.0 to 8.0

Absidia in slide culture. A cup-shaped columella (long arrow) supports a spherical sporangium (short arrow). Note also the pale tan sporangiospores (arrowhead) recently released from a sporangium

Low power photomicrograph of  Absidia in slide culture. Internodal rhizoids are not apparent here.

Photographs and captions courtesy of: UCSF Medical Center

Health Effects

Absidia mould is one of the three most common genera that can cause zygomycosis - an acute inflammation of soft tissues accompanied  with fungal invasion of the blood vessels. Zygomycosis is a rapidly fatal disease caused by several different fungal mould species. Absidia is also a common cause of rhinocerebral infections.

Underlying health conditions cause susceptibility to Absidia infection. Conditions that might predispose to infection are:

• diabetes

• severe burns

• immunosuppression

• intravenous drug use

These fungi have a tendency to invade blood vessels (particularly arteries) and enter the brain via the blood vessels. Rhinocerebral infections usually occur suddenly, rapidly, and with great severity or intensity and are frequently fatal. Death can occur very quickly.

An uncontrolled diabetic patient may become comatose and exhibit a cotton-like growth on the roof of the mouth or in the nose. These growths are the hyphae - slender, tubular threads which may be septate or nonseptate (i.e. without cross-walls)

Absidia mould 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 Absidia species. The sites of infection are the lung, nasal sinus, brain, skin and eye. (Fungal infection of the eyes can lead to blindness). Infection may have multiple sites. Absidia cormbifera has been an invasive infection agent in AIDS and neutropenic patients, as well as, agents of abortions in pigs, and subcutaneous abscesses in cats.

Therapy

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 consistently active against Absidia corymbifera. In general, Absidia is resistant to azoles. 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).

Acknowledgment

The mycological information gathered and organized in this extensive research on different pathogenic moulds was  sourced from the informative websites listed below:

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