Aspergillus terreus
Aspergillus terreus | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Eurotiomycetes |
Order: | Eurotiales |
Family: | Aspergillaceae |
Genus: | Aspergillus |
Species: | A. terreus
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Binomial name | |
Aspergillus terreus |
Aspergillus terreus, also known as Aspergillus terrestris, is a fungus (mold) found worldwide in soil. Although thought to be strictly asexual until recently, A. terreus is now known to be capable of sexual reproduction.
Aspergillus terreus can cause
In 2023, Australian scientists discovered the ability of A. terreus to decompose polypropylene plastic completely in 140 days.[7]
Appearance
Aspergillus terreus is brownish in colour and gets darker as it ages on culture media.[3][8] On Czapek or malt extract agar (MEA) medium at 25 °C (77 °F), colonies have the conditions to grow rapidly and have smooth-like walls. In some cases, they are able to become floccose, achieving hair-like soft tufts.[9] Colonies on malt extract agar grow faster and sporulate more densely than on many other media.[8]
Aspergillus terreus has conidial heads that are compact, biseriate, and densely columnar, reaching 500 × 30–50 μm in diameter. Conidiophores of A. terreus are smooth and hyaline up to 100–250 × 4–6 μm in diameter. The conidia of A. terreus are small, about 2 μm in diameter, globose-shaped, smooth-walled, and can vary from light yellow to hyaline.[10] Unique to this species is the production of aleurioconidia, asexual spores produced directly on the hyphae that are larger than the phialoconidia (e.g. 6–7 μm in diameter). This structure might be influential in the way A. terreus presents itself clinically as it can induce elevated inflammatory responses.[4][11][12]
This fungus is readily distinguished from the other species of Aspergillus by its cinnamon-brown colony colouration and its production of aleurioconidia. A. terreus is a thermotolerant species since it has optimal growth in temperatures between 35–40 °C (95–104 °F), and maximum growth within 45–48 °C (113–118 °F).[13]
Ecology
Aspergillus terreus, like other species of Aspergillus, produces spores that disperse efficiently in the air over a range of distances.[14][15] The morphology of this fungus provides an accessible way for spores to disperse globally in air current.[16] Elevation of the sporulating head atop a long stalk above the growing surface may facilitate spore dispersal through the air.[17] Normally, spores in fungi are discharged into still air, but in A. terreus, it resolves this problem with a long stalk and it allows the spores to discharge into air currents like wind.[18] In turn, A. terreus has a better chance to disperse its spores amongst a vast geography which subsequently explains for the worldwide prevalence of the fungus.
Despite A. terreus being found worldwide in warm, arable soil, it has been located in many different habitats such as compost and dust.
Genome
The Broad Fungal Genome Initiative funded by the
The
Infection
Aspergillus terreus is not as common as other Aspergillus species to cause opportunistic infections in animals and humans. However, the incidence of A. terreus infection is increasing more rapidly than any other Aspergillus and for this reason it is considered an emerging agent of infection.[24]
As an opportunistic pathogen, it is able to cause both systemic and superficial infections.
Aspergillus terreus has no adaptation in terms of changing its physical structure when infecting a human or animal host. The fungus continues to grow as the characteristic hyphae filaments. Other pathogenic fungi usually switch over to a different growth stage, mycelia-to-yeast conversion, to best suit their new environment. This process does not occur in A. terreus.[17]
Plants
For decades, A. terreus has been used in agriculture as a means to control pathogenic fungi from destroying crops. However, during the late 1980s, researchers described A. terreus as a fungal pathogen in plants. Crops such as wheat and
Aspergillus terreus has also been shown to disrupt the male sexual reproductive cycle in the plant model organism Arabidopsis thaliana. Its
Animals
Aspergillus terreus can cause infection in animals, but it is contained to a few species, such as dogs and cattle. Widely, A. terreus is found to cause mycotic abortion in cattle.[9][10][17] In dogs, especially in the German Shepherd breed, this fungus is also responsible for sinusitis.[17] It can further affect dogs through its dissemination. It can affect other parts of the body, including organs such as the spleen and kidneys.[9] Also, the bone can be affected by A. terreus which could lead to spinal osteomyelitis.[12]
Very few animal models exhibit A. terreus infections. Some successful animal models include the mouse and rabbit where A. terreus has formed pulmonary aspergillosis. These studies are important because it provides evidence that this fungal infection can cause disease.[29]
Humans
In humans, A. terreus is less commonly encountered as a pathogen than other Aspergillus species, most notably A. fumigatus, A. flavus and A. niger.[24][26] Although less frequently seen in clinical samples, A. terreus displays evidence of amphotericin B resistance which correlates to a high rate of dissemination and an overall poor prognosis.[24][30]
Aspergillus terreus causes opportunistic infections mostly in immunocompromised people such as COPD patients who are taking
Aspergillus terreus infection can lead to superficial infections in humans. These affect the outside layer of the body. It is commonly isolated from onychomycosis which is infection of human skin and nails.[9][10] The incidence of onychomycosis as a result of A. terreus (not the common agent dermatophyte) is increasing. This happens to be the most frequently reported superficial infection in clinics and hospitals.[25] Another common superficial infection caused by A. terreus includes otomycosis (ear infection), which is mostly isolated from patients who had recent surgical operations.[4][10]
In addition, A. terreus infection can also result in four main systemic disease outcomes:[3]
- Allergic bronchopulmonary aspergillosis
- Aspergillus bronchitis and invasive Aspergillus tracheobronchitis
- Invasive (pulmonary) aspergillosis
- Disseminated aspergillosis
Though all four disease outcomes can impose a great health risk to humans; invasive aspergillosis tends to result in the highest mortality and morbidity rates in humans.
Treatment and prevention
Treatment of A. terreus is clinically challenging due to its nearly complete resistance to amphotericin B, the fallback drug for serious fungal infections.[12][24] However, some newer drugs, such as voriconazole, posaconazole, and caspofungin, have shown promise in treating this agent.[32]
The laboratory identification of A. terreus from clinical specimens can also be difficult. Currently, no rapid immunological tests are available for this species, and its correct identification remains dependent on culture. A. terreus strains have a tendency to mutate while in the animal host, resulting in a substantial reduction or loss of characteristic spore heads in primary culture. Such strains continue to produce small aleuroconidia similar in appearance to the aleurioconidia of Blastomyces dermatitidis.
In one study, nearly a third of A. terreus infections in hospitals were found to be associated with the presence of potted plants.[24] Elimination of potted plants in the rooms of immunodeficient patients may have a role in prevention of illness. A. terreus has also been described in many studies as common to the hospital setting because of outside hospital construction and renovations. The amount of soil and debris reintroduced into the air is capable of travelling through the air and infecting immunosuppressed patients.[33] A simple way to take preventive action is to provide good air filtration and ventilation throughout the hospital rooms. Elimination of inoculum is key to the prevention of nosocomial infection by A. terreus.[34]
Industrial uses
Aspergillus terreus produces a number of secondary metabolites and
It is also used to produce the drug simvastatin that is chemically related to lovastatin.[38]
References
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- ^ a b c d e "Aspergillus terreus". University of Minnesota. Archived from the original on 23 September 2015. Retrieved 13 October 2013.
- ^ "Aspergillus terreus". Doctor of Fungus. Archived from the original on 3 December 2013. Retrieved 14 October 2013.
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- Australian Broadcasting Corporation News. Retrieved 26 April 2023.
- ^ a b Samson, R.A.; Hoekstra, E.S.; Frisvad, J.C. (2004). Introduction to food- and airborne fungi.
- ^ a b c d "ASPERGILLUS TERREUS" (PDF). IMI Descriptions of Fungi and Bacteria No. 1253. Retrieved 14 October 2013.
- ^ a b c d "ASPERGILLUS TERREUS" (PDF). C.M.I. Descriptions of Pathogenic Fungi and Bacteria No. 95. Retrieved 13 October 2013.
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- ^ a b "Aspergillus". Retrieved 9 November 2013.
- ^ "FUNGI REPRODUCING ASEXUALLY BY MEANS OF CONIDIA". New Brunswick Museum. Archived from the original on 13 November 2013. Retrieved 10 November 2013.
- ^ a b c d e f Summerbell, Richard. "Lecture 9 – Opportunistic mycoses I: Aspergillosis, Sporotrichosis, Zygomycosis & Rhinosporidiosis" (PDF). Archived from the original (PDF) on 2013-12-02.
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