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Aspergillus flavus – Definition, Structure, Characteristics, Habitat

Aspergillus flavus is a type of fungus that is widely distributed all over the world. It is a saprotrophic and pathogenic species that mainly colonizes cereal grains, legumes, and tree nuts. Typically, postharvest rot develops during harvest, storage, and/or transit. Its name flavus comes from the Latin word meaning yellow because of the color of its spores. This fungus can infect plants in the field, but it usually remains dormant and shows no symptoms until postharvest storage or transport. Aside from causing preharvest and postharvest infections, many strains of A. flavus produce toxic compounds called mycotoxins that can be harmful to mammals when consumed. Moreover, A. flavus is also an opportunistic pathogen that can cause aspergillosis in humans and animals with weakened immune systems. This condition is often fatal if left untreated, making it a serious concern for public health.

Aspergillus flavus, a saprophytic fungus, is known to cause diseases in plants, including grains, cereals, trees, and nuts. It is the second most common species of Aspergillus found in humans, following Aspergillus fumigatus. This fungus is mildly pathogenic and can cause opportunistic infections in crops, infecting plants before and after harvest in storage rooms. During the pre-harvest stage, the infection remains dormant until harvest time, when it can cause yellowing in the infected parts of plants. Additionally, A. flavus is capable of producing mycotoxins, which can lead to poisoning in both humans and animals. Finally, the fungus is an opportunistic pathogen that can cause aspergillosis in immunocompromised individuals.

Light microscopy of Aspergillus flavus with lactophenol cotton blue
Light microscopy of Aspergillus flavus with lactophenol cotton blue. Photo: Vladimir Ostry.

Habitat of Aspergillus flavus

  • Aspergillus flavus is a type of mold that is commonly found in soil, decaying vegetation, and crops such as corn, peanuts, and cotton.
  • It can also be found in stored grains, nuts, and spices. Aspergillus flavus thrives in warm and humid environments and is commonly found in tropical and subtropical regions.
  • It can also grow in indoor environments, particularly in damp or moist areas such as bathrooms, kitchens, and basements.
  • Aspergillus flavus can produce toxic compounds called aflatoxins, which can contaminate food and pose a health risk to humans and animals. Therefore, it is important to monitor its presence and take steps to prevent its growth and spread.

The Aspergillus flavus fungus is a globally widespread organism commonly found in soil. It exists in the soil in the form of conidia or sclerotia, and in plant tissues as mycelia. Cereal grains, legumes, and tree nuts serve as hosts for this organism. As a thermotolerant fungus, it can survive on a wider range of surfaces than other fungi. The fungus thrives in high moisture environments that are hot and humid. Its optimal growth temperature is 37°C (98.6°F) and it can grow at temperatures between 12°C (54°F) and 48°C (118°F). The optimum moisture level for Aspergillus flavus growth is 14%, although this may vary depending on the crop. For instance, the fungus grows on starchy cereals at moisture levels of 13-13.2%, while for soybeans, it grows at 11.5-11.9%. Recent data suggests that sclerotia can survive in the soil under harsh environmental conditions and produce conidia and possibly ascospores, leading to a population increase during hot and dry weather conditions.

Key Points of Aspergillus flavus

  • Aspergillus flavus can be distinguished from other species by:
    • Lack of growth at 5°C
    • Rapid growth at both 25°C and 37°C
    • Production of a bright yellow-green conidial color on MEA or CYA.
  • Colony growth on CYA can vary, from rapid growth to slow growth at room temperature.
  • Most strains produce abundant conidial structures directly from the mycelium.
  • Sclerotia can dominate colony appearance and change from white to dark reddish-brown to black in color.
  • Colonies of A. flavus exhibit a brilliant orange-yellow reverse coloration after 42-48 hours of growth on AFPA.
  • AFPA medium is recommended for the detection and enumeration of A. flavus strains in nuts, corn, spices, and other commodities.
  • A. flavus produces radiate conidial heads with variable shape and size, thin finely roughened or smooth walls, and conidiophores borne from subsurface or surface hyphae.
  • Stipes can be 400mm to 1mm or more in length, and vesicles are usually spherical to subspheroidal and 20-45mm in diameter.
  • Various isolates of A. flavus require 0.2ng g^-1 molybdenum for growth and conidial formation.
  • Molybdenum deficiency depresses growth, conidial formation, dry weight, soluble protein, and the specific activities of nitrate reductase, succinic dehydrogenase, and aconitase in the fungus.
  • Prolonged incubation on AFPA beyond 4 days is not recommended because A. ochraceus and other closely related species may also produce yellow reverse coloration after this time.

Morphology of Aspergillus flavus

  • Aspergillus flavus fungi have two groups based on sclerotia formation: Group I (L-strains) with large sclerotia and Group II (S-strains) with small sclerotia.
  • Aspergillus flavus fungi have both sexual and asexual forms of reproduction.
  • Sexual reproduction leads to sclerotia formation, while asexual reproduction produces conidia spores and sclerotia.
  • Aspergillus flavus produces conidial spores that come out from phialides on conidiophore vesicles.
  • The conidia spores have a visible mycelial mat and range in size from 3 to 6 µm. They originate from the hyphal threads and the conidiophores are rough-textured and colorless.
  • The phialides that grow from the conidiophore are both uniseriate and biseriate. The mycelium is made up of thread-like septate branches that form hyphae, which have hyaline in each septae.
  • Aspergillus flavus can also undergo sexual reproduction, producing ascospores within the sclerotia, which occurs between two compatible strains with different vegetative forms that are cultured together. The hyphae are microscopic and not visible to the naked eye.
Microscopic diagram of Aspergillus flavus.Microscopic diagram of Aspergillus flavus.
Microscopic diagram of Aspergillus flavus.

Hosts

  • Aspergillus flavus is a globally found pathogen that can infect several important agricultural crops such as cereal grains, legumes, and tree nuts.
  • The pathogen can cause ear rot in corn and yellow mold in peanuts both before and after harvest.
  • Infection can occur pre-harvest, post-harvest, during storage, and during transit.
  • A. flavus can infect seedlings by sporulation on injured seeds and invade seed embryos, which reduces germination and can lead to infected seeds planted in the field.
  • The incidence of A. flavus infection increases with insect infestation and host plant stress, including stalk rot, drought, and severe leaf damage.
  • Generally, excessive moisture conditions and high temperatures of stored grains and legumes increase the occurrence of A. flavus aflatoxin production.
  • In mammals, the pathogen can cause liver cancer through consumption of contaminated feed or aspergillosis through invasive growth.

Physiological Factors Affecting Growth of the Fungus

  • Temperature: Optimum growth temperature for A. flavus is between 25-37°C. Growth can occur between 12-48°C, but the rate decreases outside the optimal range.
  • Water Activity (aw): A. flavus has a minimum aw requirement of 0.78 for growth. The optimum aw for growth ranges between 0.95-0.98. Growth rate decreases below and above the optimum range.
  • pH: The optimal pH range for A. flavus growth is 5-8. Growth can occur between pH 2.5-11.5, but the rate decreases outside the optimal range.
  • Oxygen: A. flavus is an aerobic fungus and requires oxygen for growth. The optimum oxygen level for growth is 21%.
  • Nutrients: A. flavus requires a source of carbon, nitrogen, vitamins, and minerals for growth. It can grow on a wide range of substrates, including grains, nuts, and fruits.
  • Light: A. flavus is not directly affected by light, but can grow in the presence or absence of light. However, exposure to UV light can reduce growth and aflatoxin production.

Effects of Physical Agents

  • Temperature: High temperatures can kill A. flavus. Exposure to temperatures above 60°C can cause significant reductions in growth and aflatoxin production.
  • Moisture: High moisture levels can promote fungal growth and aflatoxin production. However, extreme dryness can also inhibit fungal growth.
  • pH: Extreme pH values can inhibit the growth of A. flavus. Exposure to pH values below 4 or above 9 can significantly reduce growth and aflatoxin production.
  • Radiation: Exposure to ultraviolet (UV) light can reduce growth and aflatoxin production in A. flavus. Gamma radiation can also reduce the growth and viability of A. flavus spores.
  • Pressure: High pressure can inhibit the growth of A. flavus. Studies have shown that exposure to pressures of 400 MPa for 10 minutes can significantly reduce fungal growth and aflatoxin production.
  • Electromagnetic fields: Exposure to electromagnetic fields can affect the growth and metabolic activities of A. flavus. Some studies have shown that exposure to specific electromagnetic frequencies can inhibit the growth and aflatoxin production of A. flavus.

Cultural characteristics of Aspergillus flavus

  • Aspergillus flavus is a fungus with cultural characteristics that can help distinguish it from other fungal species.
  • It produces conidia spores that have a visible mycelial mat and a size of 3 to 6 µm.
  • The conidiophores, which originate from hyphal threads, are colorless and rough-textured.
  • The phialides on the conidiophores can be both uniseriate and biseriate.
  • Aspergillus flavus can also reproduce sexually, producing ascospores contained within sclerotia.
  • Sexual reproduction occurs between two compatible strains with different vegetative forms that are cultured together.

Culture media used for growth of  Aspergillus flavus

Growth inhibition of A. flavus caused by two yeast strains A. pullulans PP4 and A. pullulans ZD1 after 7 days of incubation at 28 °C on malt extract agar; (A)—A. flavus as a control; (B)—a dual culture of A. flavus and A. pullulans PP4; and (C)—a dual culture of A. flavus and A. pullulans ZD1.
Growth inhibition of A. flavus caused by two yeast strains A. pullulans PP4 and A. pullulans ZD1 after 7 days of incubation at 28 °C on malt extract agar; (A)—A. flavus as a control; (B)—a dual culture of A. flavus and A. pullulans PP4; and (C)—a dual culture of A. flavus and A. pullulans ZD1.
  • Sabouraud Dextrose Agar (SDA)[Sabouraud Dextrose Agar, also known as SDA, is a type of gel-like substance used to grow microorganisms like bacteria and fungi. It’s made up of a mixture of ingredients that provide food for the microorganisms, and it’s often used in laboratories to help scientists study and identify different types of microorganisms. Just like how people need food to grow and stay healthy, microorganisms need a good environment to grow and multiply, and SDA provides that environment. It’s kind of like a playground for microorganisms, where they can grow and play and be studied by scientists.] is commonly used for the isolation and cultivation of various fungi, including Aspergillus flavus. The colonies of Aspergillus flavus grown on SDA are white and soft, with a velvety texture that gradually turns yellowish-green due to the presence of a pigment in the conidial spores.
(A) Obverse view of Aspergillus flavus on Sabouraud dextrose agar (SDA) culture tube; (B) reverse view of A. flavus on potato dextrose agar (PDA) culture tube; (C) 10Â microscopic view of A. flavus with lactophenol cotton blue (LCB) stain; (D) 40Â microscopic view of A. flavus with LCB stain; (E) 100Â microscopic view of A. flavus with LCB stain; (F) growth of A. flavus on PDA.
(A) Obverse view of Aspergillus flavus on Sabouraud dextrose agar (SDA) culture tube; (B) reverse view of A. flavus on potato dextrose agar (PDA) culture tube; (C) 10Â microscopic view of A. flavus with lactophenol cotton blue (LCB) stain; (D) 40Â microscopic view of A. flavus with LCB stain; (E) 100Â microscopic view of A. flavus with LCB stain; (F) growth of A. flavus on PDA.
  • Potato Dextrose Agar (PDA) is another commonly used agar for fungal isolation and cultivation. On PDA, the colonies of Aspergillus flavus show characteristic features such as green conidia and deep brown sclerotia mass.
Aspergillus flavus on PDA culture and slide.
Aspergillus flavus on PDA culture and slide.
  • Malt extract agar (MEA) is a medium that supports the growth of a wide range of fungi, including Aspergillus flavus. The colonies of Aspergillus flavus grown on MEA are smooth and gradually change to an olive-green color. The fungus also produces colorless sclerotia on this medium.
A. The A. flavus isolate colony on malt extract agar, at 37 ºC for 5 days, appears with deep or dark green in color of its top surface. B. Colony of A. flavus isolates grew on (CZA) at 37 ºC for 5 days appears with scattered yellow color of top surface without exudate.
  • Czapek yeast agar (CYA) is a selective medium used for the isolation and cultivation of Aspergillus species. The colonies of Aspergillus flavus on CYA appear after 7 days of incubation at either 25°C or 37°C, and they exhibit velutinous, grey-blue-green, and uniseriate conidial heads.
Macroscopic view of Aspergillus flavus on Czapek yeast extract agar (25 • C, 7 days). Photo: Vladimir Ostry.
Macroscopic view of Aspergillus flavus on Czapek yeast extract agar (25 • C, 7 days). Photo: Vladimir Ostry.

The life cycle of Aspergillus flavus

  • Aspergillus flavus, a fungus commonly found in soil, has the ability to survive the harsh winter season. It can exist as propagules on decaying organic matter in the form of mycelia or sclerotia, which are thick masses of mycelia.
  • When the environmental conditions are favorable, the sclerotia germinate and produce hyphae, which grow and give rise to asexual spores called conidia. These tiny spores are the means by which the fungus can spread and infect other organisms.
  • The tiny asexual spores of Aspergillus flavus, called conidia, have the ability to disperse through the air and environment via wind and insect pollinators.
  • When these spores land on grains and legumes, they can infect them by penetrating the silks of corn and entering the corn kernel.
  • Once inside, the spores begin to grow and produce even more conidia and conidiophores from the surface of the sclerotia, which serve as a source of nutrient and protection for the fungus.
  • Certain conidia may alight on leaves which have already been infested by insects, causing injury to the leaves in a process called secondary inoculation. In contrast, some spores are carried by rainwater and land on the ground, infecting oil-rich plants like peanuts and cotton seeds.

Genomics Studies of A. flavus

  • Aspergillus flavus is closely related to the species A. oryzae, which is used to produce fermented delicacies in Asia.
  • The complete genomic sequences of A. flavus and A. oryzae have been determined; each consists of 37 megabases (Mb) organised into eight chromosomes and is predicted to encode approximately 12,000 proteins.
  • A. oryzae contains a greater number of genes that code for extracellular hydrolases than A. flavus, but is otherwise remarkably similar.
  • Only 43 genes are unique to A. flavus and 129 genes are unique to A. oryzae; 709 genes were found to be polymorphic between the two species.
  • Numerous non-aflatoxin-producing A. flavus isolates are associated with crops, and their relationship to A. oryzae, which has been considered a distinct species for a long time, is ambiguous.
  • The increased number of genes encoding secretory hydrolytic enzymes, proteins involved in amino acid metabolism, and amino acid/sugar uptake transporters in A. oryzae compared to A. flavus supports the notion that the domestication of A. oryzae as a species better adapted for fermentation resulted in gene expansion.
  • A. flavus genomic studies have improved our understanding of secondary metabolism and its regulation.
  • 55 putative secondary metabolite clusters, including siderophores and genes involved in the biosynthesis of known A. flavus toxins, have been identified in A. flavus.
  • Overproduction of a particular gene product that may be involved in modulating vegetative growth and is flanked by genes encoding a chitin synthase activator and a cell wall glucanase correlates with repression of aflatoxin biosynthesis.
  • Comparing aflatoxin-conducive and nonconducive temperatures for growth revealed that expression of the regulatory genes aflR and aflS(J) was unaffected by temperature, indicating that the nonconducive temperature for aflatoxin production affects the stability of a key protein required for biosynthesis.

Pathogenesis and Clinical manifestations of Aspergillus flavus

Aspergillus flavus is a type of fungus that can cause a variety of diseases in humans, including invasive aspergillosis, allergic bronchopulmonary aspergillosis, and aspergilloma.

Pathogenesis

The primary route of infection is through inhalation of spores from contaminated soil, decaying plant material, or moldy food. Once inhaled, the spores can settle in the lungs and start to grow. Invasive aspergillosis occurs when the fungus invades and spreads beyond the lungs to other organs in the body, such as the brain, liver, or kidneys. The fungus produces toxins called aflatoxins, which can cause liver damage and increase the risk of developing liver cancer.

Clinical manifestations

The clinical manifestations of Aspergillus flavus infection can vary depending on the type and severity of the disease.

  1. Invasive aspergillosis: Patients with invasive aspergillosis may experience fever, chest pain, cough, shortness of breath, and fatigue. In severe cases, the infection can spread to other organs and cause symptoms such as confusion, seizures, and organ failure.
  2. Allergic bronchopulmonary aspergillosis: This condition typically affects patients with underlying respiratory conditions such as asthma or cystic fibrosis. Symptoms include wheezing, coughing, and shortness of breath.
  3. Aspergilloma: Aspergillomas are masses of fungus that grow in the lungs, usually in patients with pre-existing lung damage such as tuberculosis or bronchiectasis. Symptoms can include coughing up blood, chest pain, and shortness of breath.

Human Aspect of Aspergillus flavus infection

  • “Aspergillus flavus can cause a lung infection called invasive aspergillosis. The tiny conidial spores of this fungus stick to the bottom layer of lung cells, which is called the basal lamina. This fungus likes certain proteins, such as fibrinogen, which help it stick to the basal lamina. Some other proteins, like fibronectin, laminin, and complement, can also make the infection worse. Additionally, albumin and surfactant proteins can attract Aspergillus flavus.”

What is Aspergillosis?

  • Aspergillus flavus is a type of fungus that can cause a number of different health problems in humans. It is the second most common cause of invasive and noninvasive aspergillosis, which can affect the lungs and other parts of the body. Aspergillus flavus is also the most common cause of a type of infection called superficial infection.
  • The symptoms of aspergillosis vary depending on the type of infection that occurs. Some people may experience allergic reactions, which can cause symptoms like asthma, inflammation in the lungs, or allergic bronchopulmonary aspergillosis. Others may develop a more serious condition known as invasive infection, which can affect the lungs and other parts of the body. Other symptoms may include chronic granulomatous sinusitis, keratitis, cutaneous aspergillosis, wound infections, and osteomyelitis following trauma and fungal inoculation.
  • Aspergillus flavus spores are found in the air we breathe and can easily be inhaled into the lungs. Large spores can become lodged in the upper respiratory tract, leading to fungal sinusitis. People who have weakened immune systems, like transplant patients, are more likely to develop aspergillosis. Secondary transmission of fungal spores can arise from infection via wounds and smoking contaminated plant material such as tobacco or marijuana.
  • Overall, it is important to be aware of the potential health risks associated with Aspergillus flavus and take steps to protect yourself from exposure.

Aflatoxicosis

  • The toxicity of the fungi is exacerbated by the consumption of aflatoxins that they produce. Aflatoxins B1 and B2 are commonly produced by the fungi’s sclerotia forms.
  • However, the S strain of the fungi produces aflatoxins G1 and G2, which are not commonly produced by A.flavus. While the L strain of the fungi is more aggressive than the S strain, it produces fewer aflatoxins, fewer sclerotia, and is more acidic.
  • The carcinogenic nature of the aflatoxins causes aflatoxicosis, which is associated with a range of symptoms including vomiting, abdominal cramping and pain, pulmonary edema, hemorrhaging, disruption of food digestion, poor abdominal absorption and metabolism, and severe progressive effects that may cause liver damage, liver cancer, mental impairment, coma, and death.

Carcinogenic effects of aflatoxins

  • Cancers that develop due to long-term exposure to aflatoxin B1, a potential hepatocarcinogen, have been studied extensively.
  • Aflatoxin B1 induces tumors, particularly in the liver, but also in other organs like the kidney, lungs, and colon, both in humans and animals. Consumption of aflatoxin B1 has been closely associated with primary liver cancer or hepatocellular carcinoma (HCC).
  • Aflatoxin associated HCC has been observed more frequently in individuals with chronic Hepatitis B and C, where the two conditions synergistically interact and increase the development of HCC.
  • It is therefore critical to be aware of these risks and take appropriate measures to avoid or reduce exposure to aflatoxin B1, particularly in individuals who have chronic Hepatitis B and C.

Plant pathologies

  • The colonization of plants by Aspergillus flavus can be facilitated by several factors such as the mode of dispersion and damage inflicted by plant and insect eaters.
  • The insects and plants themselves provide a point of entry for the fungi into the plants while the insects and blowing wind enable the spores to land on the damaged surfaces of these plants, leading to the growth of the fungi which then become dormant until the plants are harvested and stored.
  • Subsequently, during storage, the fungi can germinate and spread within the crop and surrounding crops.
  • Colonization of plants by Aspergillus flavus can be identified by the formation of powdery masses of yellowish-green spores on the upper surface and reddish-gold on the lower surface.
  • In both grains and legumes, the infection is generally limited to small areas, and affected areas often show discoloration and dullness. Colonies appear downy or powdery in texture, and growth is rapid.

Aspergillus Ear Rot

  • Aspergillus flavus is responsible for producing aflatoxins that result in this condition. A powdery olive-green (yellow-green) mold proliferates on the ears of corn, and its color changes to brown as it ages.
  • The presence of discolored, shrunken kernels, which are commonly found near the tip of the ear, is linked to higher levels of aflatoxins.
  • The disease thrives in hot, dry conditions during pollination and grain filling, and it primarily infects yellow-brown silks.
  • When spores settle on the silks, they germinate, rapidly grow down the silk, and then colonize the surface of the developing kernels. As the plant matures and the moisture levels decrease to <15%, the fungi spread to the internal tissues and continue to proliferate.

Diversity in A. flavus Populations

  • Populations of Aspergillus flavus are diverse and constituted of vegetative compatibility groups (VCGs).
  • VCGs limit genetic exchange between VCGs and restrict hyphal fusion to genotypes within the same VCG.
  • New VCGs may arise as a result of random mutations at compatibility loci, or through genetic recombination.
  • A population of A. flavus from Georgia demonstrates a lengthy history of recombination.
  • By rearranging genes, it is possible to produce progeny with a novel genomic structure that is vegetatively incompatible with both parental and sibling strains.
  • A population undergoing constant recombination will eventually contain individuals with numerous VCGs.
  • A. flavus isolates from distinct VCGs can vary in enzyme production, virulence, and aflatoxin-producing capacity.
  • A. flavus has been classified into two sclerotial morphotypes, S (small) and L (large), based on the size disparities of their sclerotia.
  • Recent phylogenetic research indicates that these morphotypes diverged independently from an aflatoxin B- and G-producing ancestor.
  • S-group isolates produce more sclerotia and fewer conidia than L-group isolates and respond differentially to pH, growth, and differentiation in light and dark environments. The ‘typical’ A. flavus strain L produces fewer sclerotia but more conidia when grown under identical conditions.

Laboratory Diagnosis Methods for Aspergillus flavus

Aspergillus flavus is a common fungus that can cause various diseases in humans, including aspergillosis, a serious lung infection. Laboratory diagnosis of Aspergillus flavus can be done using various methods, including:

  1. Microscopy: Microscopic examination of clinical specimens can reveal the presence of Aspergillus flavus. The fungus has distinctive features, including septate hyphae with dichotomous branching and conidiophores with uniseriate phialides.
    • KOH wet mount: A KOH wet mount is a test that helps doctors and scientists look at tiny things that might be growing on your skin, hair or nails. Here’s how it works: First, a small sample of the affected area is collected. Then, a special liquid called potassium hydroxide (KOH) is added to the sample. The KOH helps dissolve the skin cells and makes it easier to see any fungi or bacteria that might be causing the problem. Once the sample is prepared, it is looked at under a microscope to identify any signs of infection. The KOH wet mount is a quick and painless test that can help doctors diagnose many different skin conditions, such as ringworm or athlete’s foot.
  2. Culture: Aspergillus flavus can be grown on various culture media, including Sabouraud agar, potato dextrose agar, and Czapek’s agar. The fungus produces colonies that are greenish-yellow in color and have a characteristic musty odor.
    • Sabouraud Dextrose Agar is a type of culture medium used to grow fungi, and it has different characteristics depending on the type of fungi being grown. When growing certain types of fungi, like Aspergillus flavus, the colonies start out as white and soft with a velvety surface. As they continue to grow over the course of several days, they become raised and floccose at the center, and turn yellowish-green when they start to sporulate. Sclerotia are also produced, which appear initially as white, but turn brown after six days of growth. The colonies are relatively large, ranging from 55-70mm in diameter.
    • Potato Dextrose Agar is another type of culture medium that produces different characteristics depending on the type of fungi being grown. When growing certain types of fungi, the colonies appear green due to the color of the conidia. They are plain and flat at the edges, but raised at the center with a wrinkled cerebriform pattern. They also produce colorless or brown exudates, and deep brown sclerotia. The colonies are encircled by a white border and a pale inner side.
    • Malt extract agar is yet another type of culture medium used to grow fungi. The colonies that form on this medium vary in shape and size, starting out as smooth white mycelia, and later producing olive and dark green conidia. Sclerotia are also produced, and appear as white and deep brown with colorless exudates at the center of the colonies.
    • Finally, Czapek yeast agar is a type of culture medium that produces different characteristics depending on the type of fungi being grown. When growing certain types of fungi, the mycelia are white, flat with large raised tufted wool of white mycelia. The colonies appear dry and exudated, but no sclerotia are produced. The colonies are uncolored, although some isolates produce velutinous, grey-blue-green, and uniseriate conidial heads.
  3. Molecular methods: Polymerase chain reaction (PCR) and DNA sequencing can be used to identify Aspergillus flavus directly from clinical specimens or culture isolates. PCR-based assays can detect specific genes or regions of the fungal genome, such as the internal transcribed spacer (ITS) region.
  4. Serology: Detection of specific antibodies against Aspergillus flavus can be done using serological methods, such as enzyme-linked immunosorbent assay (ELISA) or immunodiffusion tests. However, these tests have limited sensitivity and specificity and should be used in conjunction with other diagnostic methods.
  5. Histopathology: Examination of tissue samples using histopathological techniques can reveal the presence of Aspergillus flavus in affected tissues. The fungus appears as septate hyphae with dichotomous branching and may produce characteristic fruiting bodies called aspergillomas.

Economic Importance of Aspergillus flavus

Aspergillus flavus has both positive and negative economic impacts:

Positive:

  • Production of aflatoxin by A. flavus has been exploited as a natural pesticide against agricultural pests, such as termites and weevils.
  • A. flavus is used in the production of various fermented foods, including tempeh, soy sauce, and some types of miso.
  • A. flavus has been studied for its potential use in bioremediation of soil and water contaminated with toxic compounds.

Negative:

  • A. flavus is a major cause of economic losses in agriculture due to its ability to produce aflatoxins, which can contaminate crops such as peanuts, corn, and cottonseed, rendering them unsuitable for human or animal consumption.
  • Aflatoxin contamination can also lead to trade barriers and reduced export opportunities for affected countries.
  • In addition to crop losses, A. flavus can cause spoilage of stored grains, resulting in additional economic losses.
  • The health impacts of aflatoxin contamination, including liver cancer and immune suppression, can lead to increased healthcare costs and decreased workforce productivity.
  • In the pharmaceutical industry, A. flavus can produce unwanted secondary metabolites that can affect drug safety and efficacy.

Treatment of Aspergillus flavus infections

The treatment of Aspergillus flavus infections depends on several factors, including the severity of the infection, the site of infection, and the patient’s overall health status. Treatment may include the following:

  1. Antifungal medications: The mainstay of treatment for Aspergillus flavus infections is antifungal medications, including azoles, echinocandins, and amphotericin B. The choice of medication depends on the site and severity of the infection, as well as the patient’s overall health status. Invasive infections may require long-term treatment with antifungal medications.
  2. Surgical intervention: In some cases, surgical intervention may be necessary to remove infected tissue or drain abscesses. This is especially true in cases of invasive aspergillosis, which can be life-threatening.
  3. Supportive care: Patients with Aspergillus flavus infections may require supportive care, such as oxygen therapy, mechanical ventilation, or nutritional support. This is especially true in cases where the infection has spread to the lungs.
  4. Prevention: Prevention is important for patients who are at risk of Aspergillus flavus infections, such as those with weakened immune systems. This may include measures such as antifungal prophylaxis, infection control measures, and avoiding environmental sources of the fungus.

Prevention and Control

Prevention and control of Aspergillus flavus infections can be achieved through a combination of measures, including:

  1. Infection control measures: Hospitals and healthcare facilities should have infection control protocols in place to prevent the spread of Aspergillus flavus infections. This may include measures such as isolation of infected patients, use of personal protective equipment, and proper cleaning and disinfection of equipment and surfaces.
  2. Environmental control: Aspergillus flavus is a ubiquitous fungus that can be found in the environment. Measures such as proper ventilation, moisture control, and elimination of potential sources of contamination, such as moldy or contaminated food, can help reduce the risk of exposure.
  3. Prophylaxis: Patients who are at high risk of Aspergillus flavus infections, such as those undergoing bone marrow transplantation or receiving chemotherapy, may benefit from antifungal prophylaxis.
  4. Immunomodulatory therapy: Immunomodulatory therapy may be used to boost the immune system and reduce the risk of Aspergillus flavus infections in patients with weakened immune systems.
  5. Education: Education of healthcare workers, patients, and their families about the risk of Aspergillus flavus infections, as well as the importance of proper hygiene and infection control measures, can help reduce the incidence of infections.

FAQ

What is Aspergillus flavus?

Aspergillus flavus is a species of fungus that is commonly found in soil, decaying vegetation, and agricultural crops, particularly in warm and humid environments. It is known to produce a carcinogenic mycotoxin called aflatoxin, which can contaminate food crops and cause serious health problems in humans and animals.

What is the main concern regarding Aspergillus flavus?

The main concern regarding Aspergillus flavus is its ability to produce aflatoxins, which are potent carcinogens that can cause liver cancer and other health problems in humans and animals if consumed in contaminated food products.

What type of diseases can Aspergillus flavus cause in humans?

Aspergillus flavus can cause a range of respiratory diseases, including aspergillosis, which is an infection of the lungs or other organs. It can also cause allergic reactions in some people.

How is Aspergillus flavus diagnosed?

Aspergillus flavus infections can be diagnosed through a combination of clinical examination, radiological imaging, and laboratory tests, such as culture and microscopy of sputum, bronchoalveolar lavage (BAL) fluid, or other body fluids.

What is the treatment for Aspergillus flavus infections?

Treatment for Aspergillus flavus infections typically involves the use of antifungal medications, such as voriconazole or amphotericin B, administered either orally or intravenously. In some cases, surgical intervention may also be required.

How can Aspergillus flavus be prevented?

Preventing Aspergillus flavus contamination requires a combination of measures, including proper storage and handling of food products, proper ventilation in agricultural and industrial settings, and the use of fungicides and other preventive measures in crops and agricultural fields.

Where is Aspergillus flavus commonly found?

Aspergillus flavus is commonly found in soil, decaying vegetation, and agricultural crops, particularly in warm and humid environments. It is often found in crops such as peanuts, maize, and cottonseed.

What are the key features of Aspergillus flavus growth on culture media?

Aspergillus flavus can be readily distinguished from other Aspergillus species by its lack of growth at 5°C and rapid growth at both 25 and 37°C, and by the production of a bright yellow-green conidial coloration when cultured on malt extract agar (MEA) or Czapek yeast extract agar (CYA).

What factors affect the growth of Aspergillus flavus?

Several factors can affect the growth of Aspergillus flavus, including temperature, moisture, pH, radiation, pressure, and electromagnetic fields.

Can Aspergillus flavus be beneficial in any way?

While Aspergillus flavus is primarily known for its ability to produce aflatoxins, it also has some beneficial uses. It can be used in the production of certain enzymes, such as amylases and proteases, and has potential applications in bioremediation and other environmental processes.

References

  • Dobson, A. D. W. (2002). ASPERGILLUS FLAVUS. Encyclopedia of Dairy Sciences, 116–122. doi:10.1016/b0-12-227235-8/00031-6
  • Jackson, S. A., & Dobson, A. D. W. (2016). Yeasts and Molds: Aspergillus flavus. Reference Module in Food Science. doi:10.1016/b978-0-08-100596-5.01086-6
  • Bhatnagar, D., Cleveland, T. E., & Payne, G. A. (1999). ASPERGILLUS | Aspergillus Flavus. Encyclopedia of Food Microbiology, 72–79. doi:10.1006/rwfm.1999.0065
  • Bhatnagar, D., Ehrlich, K. C., Moore, G. G., & Payne, G. A. (2014). ASPERGILLUS | Aspergillus flavus. Encyclopedia of Food Microbiology, 83–91. doi:10.1016/b978-0-12-384730-0.00012-4
  • Hedayati MT, Pasqualotto AC, Warn PA, Bowyer P, Denning DW. Aspergillus flavus: human pathogen, allergen and mycotoxin producer. Microbiology (Reading). 2007 Jun;153(Pt 6):1677-1692. doi: 10.1099/mic.0.2007/007641-0. PMID: 17526826.
  • https://www.cifr.ncsu.edu/aflavus/
  • https://en.wikipedia.org/wiki/Aspergillus_flavus

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0 thoughts on “Aspergillus flavus – Definition, Structure, Characteristics, Habitat”

  1. What are some of the ways that Aspergillus flavus populations can differ and how does this impact their enzyme production, virulence, and aflatoxin-producing ability?

    Reply
    • Aspergillus flavus is a species of fungi that can be found in soil, decaying vegetation, and crops such as corn, peanuts, and cottonseed. While some strains of A. flavus are benign, others are capable of producing aflatoxins, which are potent carcinogenic compounds that can contaminate food and feed.

      Genetic diversity: A. flavus is a highly diverse species, with variations in its genome leading to different strains and subpopulations. These genetic differences can impact the fungi’s virulence and ability to produce aflatoxins.

      Geographical location: A. flavus populations can vary based on the geographic location where they are found. Different environments can result in different microbial communities and nutrients available for the fungi to thrive on, which can impact their enzyme production and aflatoxin-producing ability.

      Host species: A. flavus can infect various plant species, and the different plant species can influence the growth and metabolism of the fungi. This can result in differences in their enzyme production and ability to produce aflatoxins.

      Environmental conditions: Temperature, humidity, and other environmental factors can impact A. flavus growth and aflatoxin production. For example, higher temperatures and increased moisture levels can promote aflatoxin production.

      The differences in A. flavus populations can have significant impacts on their enzyme production, virulence, and aflatoxin-producing ability. For example, some strains of A. flavus are highly virulent and can cause disease in plants and animals, while others are less harmful. The ability to produce aflatoxins is also highly variable, with some strains capable of producing high levels of toxins while others produce little or none.

      Additionally, the enzyme production of A. flavus can vary depending on the strain, host, and environmental conditions. A. flavus produces several enzymes that are involved in the degradation of plant material, such as cellulases, hemicellulases, and pectinases. These enzymes are important for the fungi to obtain nutrients from their host and play a critical role in the infection process. The expression of these enzymes can impact the severity of the disease and the ability of the fungi to infect new hosts.

      In conclusion, the differences in A. flavus populations can have significant impacts on their enzyme production, virulence, and aflatoxin-producing ability. Understanding these differences can help researchers develop strategies for controlling the spread of the fungi and preventing aflatoxin contamination in food and feed.

      Reply
  2. This is a comprehensive overview of Aspergillus flavus and its pathogenicity in both plants and animals. It’s alarming how this fungus can remain dormant and unnoticed until postharvest storage or transport. The fact that it produces mycotoxins that can be harmful to mammals is also concerning. I appreciate the information about its opportunistic pathogenicity in humans and animals with weakened immune systems. This article highlights the importance of understanding and preventing the spread of A. flavus for public health and food safety.

    Reply
  3. It is interesting to note the specific requirements for the growth of A. flavus. Considering these factors, there could be potential strategies for controlling its growth in certain environments. For instance, regulating temperature, water activity, and pH could be used to limit the growth of this fungus in food storage or processing facilities. Additionally, exploring the effect of light exposure, particularly UV light, could offer insights into new methods for preventing aflatoxin production. Further research in these areas could lead to the development of more effective approaches for managing A. flavus contamination.

    Reply

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