Aspergillus clavatus- An Overview
Aspergillus clavatus is a species of fungus that belongs to the genus Aspergillus, which comprises a large group of filamentous fungi that are widely distributed in nature and have diverse ecological roles. Aspergillus clavatus is characterized by its elongated club-shaped vesicles and its blue-green uniseriate conidia, which are the asexual spores that are produced and dispersed by the fungus. The conidia are very small, measuring about 3–4.5 x 2.5–4.5 μm, and can be easily inhaled by humans and animals.
Aspergillus clavatus was first described scientifically in 1834 by the French mycologist John Baptiste Henri Joseph Desmazières, who named it after its clavate (club-like) shape of the conidial heads. It belongs to the Aspergillus section Clavati, which includes six other species that share similar morphological features. In 2018, a sexual stage of Aspergillus clavatus was discovered and described with a Neocarpenteles teleomorph, but under the one fungus-one name convention, the original name of Aspergillus clavatus was retained.
Aspergillus clavatus is found in soil and animal manure, where it grows and thrives in humid environments and temperatures of 25°C. It can also grow in a wide range of temperatures, from 5°C to 42°C, and can tolerate low water activity. It is commonly associated with cultivated crops such as barley, potatoes, sugarcane, cotton, and legumes, as well as stored cereals such as rice, corn, and millet. It can also be found in wet or moist areas such as bathrooms, kitchens, basements, and air conditioning systems.
Aspergillus clavatus is not only an environmental fungus but also a potential pathogen and toxin producer. It can cause allergic reactions and pulmonary diseases in humans and animals who inhale its spores or come into contact with its mycelia. It can also produce mycotoxins such as patulin, tryptoquivalones, and cytochalasin E, which can have harmful effects on the health of humans and animals who consume contaminated food or drink. Besides its pathogenic and toxic properties, Aspergillus clavatus also has some beneficial aspects. It can produce antimicrobial metabolites that are used in pharmaceutical industries, such as clavatolides and clavatustatins. It can also degrade lignocellulosic biomass and produce enzymes that are useful for biotechnological applications.
Aspergillus clavatus is a species of Aspergillus group of fungi, that is widely spread in areas of humid environments in temperatures of 25°C. They grow in minimum temperatures of up to 5°C and a maximum of at least 42°C. It is majorly found in soil and animal manure. In soil, they grow and thrive in cultivated soils with barley, potatoes, sugarcane, cotton, and leguminous plants. They are also found in wet or moist areas. It can also be found in food cereals such as stored rice, corn, millet, and most especially in humid environments. Aspergillus clavatus can also colonize indoor environments, such as air conditioning systems, carpets, wallpapers, and furniture. It has been isolated from various organic materials, such as compost, hay, straw, wood chips, and paper. Aspergillus clavatus has potential biotechnology applications, as it can produce antimicrobial metabolites and enzymes that can degrade lignocellulosic biomass. However, it can also pose health risks to humans and animals, as it can produce allergens and mycotoxins that can cause respiratory and gastrointestinal diseases.
Aspergillus clavatus is a filamentous fungus that produces spores called conidia. The morphology of Aspergillus clavatus can be observed at two levels: the colony level and the microscopic level.
Aspergillus clavatus grows rapidly on various culture media, forming colonies that are initially white, but turn yellow-green as they mature. The colonies have a velvety and fairly dense texture, and may produce a strong unpleasant odor. The colonies are slightly furrowed and have a thin mycelial surface with erect conidiophores.
Aspergillus clavatus has septate hyphae that form V-shaped dichotomous branches. The hyphae give rise to specialized cells called foot cells, from which the conidiophores originate. The conidiophores are long, smooth-walled, colorless, and hyaline structures that can reach up to 3 mm in length and 20-30 μm in diameter.
The conidiophores have an enlarged vesicle at the tip, which is club-shaped or clavate, hence the name of the species. The vesicle is 200-250 μm long and 40-60 μm wide, and bears phialides over its entire surface. The phialides are flask-shaped cells that produce conidia by budding.
The conidia are elliptical, smooth, thick-walled, and greenish-olive in color. They are arranged in columns or chains that radiate from the vesicle, forming large conidial heads that are 300-400 μm by 150-200 μm when young. As the conidia mature, they split into divergent columns of two or more, forming compact and conspicuous structures that resemble a brush or a broom. The conidia are 3-4.5 μm long and 2.5-4.5 μm wide, and can be easily dispersed by air currents.
Aspergillus clavatus can grow on different media, but its morphology and growth rate may vary depending on the culture conditions. Here are some examples of how Aspergillus clavatus grows on different media:
- Czapek`s solution agar: This is a common medium for culturing Aspergillus species. Aspergillus clavatus grows rapidly on this medium, producing colonies of 3.0-3.5 cm in diameter after 8-10 days at 24-26°C. The colonies are plane or slightly furrowed, with a floccose texture and a thin mycelial surface. The conidiophores are erect and colorless at first, but turn brown with age. The conidial heads are large and clavate when young, but split into divergent columns of greenish-olive conidia when mature.
- Malt extract agar: This is another medium for culturing Aspergillus species, especially those that produce mycotoxins. Aspergillus clavatus grows less vigorously on this medium, producing smaller and weaker conidial structures. The conidiophores are short and thin, with columnar heads of 300-500 μm in length. The colonies grow within 6 days, and produce a strong unpleasant odor.
- DG-18 agar: This is a selective medium for isolating xerophilic fungi from foods and feeds. Aspergillus clavatus can grow on this medium, producing colonies of 2-3 cm in diameter after 7 days at 25°C. The colonies are white to pale yellow, with a velvety to powdery texture. The conidiophores are long and hyaline, with clavate vesicles and phialides covering the entire surface. The conidia are smooth-walled and ellipsoidal.
Here are some images of Aspergillus clavatus colonies on different media:
|Czapek`s solution agar
|Malt extract agar
Aspergillus clavatus reproduces asexually by producing conidia, which are spores that are formed on specialized structures called conidiophores. The conidiophores are hyphae that branch from the mycelium and bear a swollen vesicle at the tip. The vesicle is covered with phialides, which are flask-shaped cells that produce chains of conidia. The conidia are spherical, smooth, and thick-walled, and have a bluish-green color. The conidia are dispersed by air currents and can survive in various environments.
When the conidia land on a suitable substrate, such as soil, plant material, or animal manure, they germinate and produce germ tubes that grow into hyphae. The hyphae form a network of filaments called the mycelium, which is the vegetative part of the fungus. The mycelium can grow rapidly and colonize various organic substrates. The mycelium can also produce more conidiophores and conidia, completing the asexual cycle.
Aspergillus clavatus also has a sexual cycle, which was discovered in 2017 by researchers who found evidence of mating-type genes and sexual structures in the fungus. The sexual cycle involves the fusion of two compatible hyphae of opposite mating types (MAT1-1 and MAT1-2), which are determined by the presence of different alleles of a single gene. The fusion results in the formation of a heterokaryotic hypha, which contains nuclei from both parents. The heterokaryotic hypha then produces a fruiting body called a cleistothecium, which is a spherical structure that encloses the sexual spores called ascospores. The cleistothecium is fawn to brown/yellow in color and contains about 100 to 200 ascospores. The ascospores are heat-resistant and can survive harsh conditions. They are released when the cleistothecium ruptures or decays, and can germinate to produce new mycelia, completing the sexual cycle.
The life cycle of Aspergillus clavatus is shown in the following diagram:
Aspergillus clavatus is a fungus that can produce the toxin patulin, which may be associated with disease in humans and animals. This species is only occasionally pathogenic, but it is allergenic, causing the occupational hypersensitivity pneumonitis known as malt-worker`s lung.
Aspergillus clavatus produces dry, hydrophobic spores that are easily inhaled by humans and animals. Due to the small size of the spores, about 70% of them are able to penetrate into the trachea and primary bronchi and close to 1% into alveoli. Inhalation of spores of Aspergillus clavatus poses a health risk, especially for people with mold allergies or immunocompromised conditions.
The clinical manifestations of Aspergillus clavatus infection include:
- Allergic aspergillosis: This is an IgE-mediated hypersensitivity reaction to fungal spores produced by Aspergillus clavatus. It occurs due to repeated exposure to conidial spores of Aspergillus clavatus. After frequent exposure, the body mounts a hypersensitivity immune response that damages the surrounding tissues causing lung diseases, illnesses of the airway, and digestive illnesses when ingested often.
- Pulmonary aspergillosis: This is a spectrum of pulmonary clinical diseases with impaired and excessive immune reactions. It involves an excessive inflammatory response to hyphae colonizing the sinopulmonary tract. It can manifest as invasive aspergillosis, chronic necrotizing aspergillosis, or aspergilloma.
- Malt worker`s lung: This is an occupational disease caused by frequent exposure to conidial spores in large amounts. It affects farmers working with barley plantations. Barley releases millions of spores during brewing (malting) and frequent and excessive exposure causes the Malt worker`s lung disease. Symptoms range from acute to sub-acute and occasionally chronic. Acute symptoms include coughing, tightening of the chest associated with difficulty breathing. Progressive disease is associated with extrinsic allergic alveolitis, with fever, chills, malaise, headaches, coughing, difficulty breathing, loss of appetite, loss of weight, malaise. If not treated in this stage, it can lead to Chronic disease which comprises a compromised respiratory system, respiratory distress, hypoxia, body wasting, and at this stage the disease is irreversible.
- Nail and skin infections: Aspergillus clavatus can also cause superficial infections of the nails and skin, such as onychomycosis and dermatomycosis.
- Patulin toxicity: It occurs as a result of exposure to mycotoxins produced by Aspergillus clavatus. Patulin mycotoxin is produced in rotten apples and apple products like juice, apple jams, and apple cider. They can also be found in berries, bananas, plums, and cherries. Patulin causes gastrointestinal irritation when ingested causing stomach pains, vomiting, and diarrhea that may lead to difficulty in breathing, coughing, and fluid accumulation in the lungs. Over poisoning with patulin can cause neurotoxicity causing life-threatening convulsions and neurological deficits. Other mycotoxins produced by Aspergillus clavatus include tryptoquivalones that are produced from moldy rice which can cause death in children and cytochalasin E mycotoxin which prevents the formation of blood vessels.
Aspergillus clavatus is a fungus that can cause various diseases in humans and animals, such as allergic reactions, pulmonary infections, nail and skin infections, and mycotoxin poisoning. Laboratory diagnosis of Aspergillus clavatus is important to confirm the infection and guide the appropriate treatment. The following methods can be used for laboratory diagnosis of Aspergillus clavatus:
- Specimens: The most common specimens for diagnosis of Aspergillus clavatus are respiratory secretions, such as sputum, bronchial wash, or bronchoalveolar lavage (BAL). These specimens can be obtained from patients with suspected pulmonary aspergillosis or malt worker`s lung. Other specimens that can be used are skin scrapings, nail clippings, blood, urine, or tissue biopsies from infected sites.
- Culture: Culture is the gold standard method for identification of Aspergillus clavatus. The specimens are inoculated on suitable media, such as Czapek`s solution agar or malt extract agar, and incubated at 25°C for 7 to 10 days. The colonies of Aspergillus clavatus have distinctive morphological features, such as a bluish-green color, a velvety texture, and large club-shaped conidia heads. The conidia are arranged in columns and have a smooth and thick wall. The conidiophores are long, colorless, and hyaline.
- Microscopy: Microscopy is used to examine the stained or unstained specimens or cultures for the presence of Aspergillus clavatus filaments and conidia. The specimens can be stained with a dye, such as lactophenol cotton blue or calcofluor white, to enhance the visibility of the fungal structures. The microscopy can reveal the characteristic features of Aspergillus clavatus, such as the clavate vesicles, the phialides covering the entire surface of the vesicles, and the elliptical conidia.
- Molecular detection: Molecular detection is used to detect the DNA or RNA of Aspergillus clavatus in the specimens or cultures. This method can be more sensitive and specific than culture or microscopy, especially for low-burden or non-culturable samples. The most common molecular technique is polymerase chain reaction (PCR), which amplifies a specific region of the fungal genome and detects it by gel electrophoresis or hybridization probes. Other molecular techniques include real-time PCR, loop-mediated isothermal amplification (LAMP), or sequencing.
- Biochemical examination: Biochemical examination is used to analyze the chemical composition of the cell wall or metabolites of Aspergillus clavatus. This method can provide additional information for identification or differentiation of Aspergillus species. For example, Aspergillus clavatus has a high content of mannitol and arabitol in its cell wall carbohydrates. It also produces mycotoxins, such as patulin and cytochalasin E, which can be detected by chromatography or immunoassays.
These are some of the methods that can be used for laboratory diagnosis of Aspergillus clavatus. Depending on the availability of resources and expertise, one or more methods can be applied to confirm the infection and guide the treatment.
The treatment of diseases caused by Aspergillus clavatus depends on the type and severity of the infection, as well as the underlying health condition of the patient. Some of the possible treatment options are:
- Antifungal medications: These are drugs that can kill or stop the growth of the fungus. They can be taken orally, intravenously, or inhaled. Some examples of antifungal medications used for Aspergillus clavatus infections are itraconazole, voriconazole, amphotericin B, and nystatin. Antifungal medications are usually prescribed for allergic aspergillosis, invasive aspergillosis, and nail and skin infections.
- Corticosteroids: These are drugs that can reduce inflammation and suppress the immune system. They can be taken orally, intravenously, or inhaled. Some examples of corticosteroids used for Aspergillus clavatus infections are hydrocortisone and prednisolone. Corticosteroids are usually prescribed for allergic aspergillosis and malt worker`s lung disease.
- Surgery: This is a procedure that involves removing the infected tissue or organ. Surgery may be needed for aspergilloma, invasive aspergillosis, or patulin toxicity that does not respond to antifungal medications. Surgery may also be needed to stop bleeding in the lungs caused by pulmonary aspergillosis.
- Bronchial artery embolization: This is a procedure that involves blocking the blood vessels that supply blood to the infected area of the lung. This can help stop bleeding in the lungs caused by pulmonary aspergillosis.
- Supportive care: This includes providing oxygen therapy, fluid replacement, pain relief, and nutritional support to the patient. Supportive care can help improve the symptoms and prevent complications of Aspergillus clavatus infections.
The treatment of Aspergillus clavatus diseases should be guided by a specialist doctor who can diagnose the type of infection and prescribe the appropriate medication and dosage. The treatment duration may vary depending on the response and tolerance of the patient. The patient should follow the doctor`s instructions and complete the course of treatment to prevent relapse or resistance.
Aspergillus clavatus is a common mold that can cause various health problems, especially in people with weakened immune systems or lung diseases. To prevent and control Aspergillus clavatus infections, the following measures are recommended:
- Protect yourself from the environment. Try to avoid areas with a lot of dust or mold, such as construction sites, farms, or damp places. If you can`t avoid these areas, wear a face mask (preferably an N95 respirator) while you`re there. Wear gloves, shoes, long pants, and long-sleeved shirts when handling soil, manure, or plants that may be contaminated with Aspergillus clavatus spores. Clean any skin injuries that have been exposed to dust or soil with soap and water.
- Antifungal medication. If you are at high risk for developing invasive aspergillosis (a serious infection that spreads to other organs), your doctor may prescribe antifungal drugs to prevent it. These drugs include itraconazole and amphotericin B. You should take them as directed by your doctor and report any side effects or symptoms of infection.
- Testing for early infection. Some high-risk patients may benefit from blood tests to detect Aspergillus clavatus infection early. These tests can measure the levels of certain antibodies or antigens that indicate the presence of the fungus in the body. Your doctor can advise you if these tests are suitable for you and how often you should have them done.
- Consult specialists on mold removal. If you have mold growth in your home or workplace, you should seek professional help to remove it safely and effectively. Mold removal experts can identify the type and source of mold, use appropriate equipment and methods to eliminate it, and prevent it from coming back. You should also follow their recommendations on how to maintain a clean and dry environment that discourages mold growth.
By following these steps, you can reduce your risk of getting sick from Aspergillus clavatus and protect your health and well-being.
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