Aphanoascus fulvescens

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Aphanoascus fulvescens
Aphanoascus fulvescens ascospores.jpg
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Eurotiomycetes
Order:
Onygenales
Family:
Onygenaceae
Genus:
Aphanoascus
Species:
A. fulvescens
Binomial name
Aphanoascus fulvescens
(Cooke) Apinis (1968)
Synonyms

Badhamia fulvescensCooke (1875)

Aphanoascus fulvescens is a mould fungus that behaves as a keratinophilic saprotroph and belongs to the Ascomycota. It is readily isolated from soil and dung containing keratin-rich tissues that have been separated from their animal hosts. This organism, distributed worldwide, is most commonly found in areas of temperate climate, in keeping with its optimal growth temperature of 28 °C (82 °F). While A. fulvescens is recognized as a geophilic fungal species, it is also a facultative opportunistic pathogen. Although it is not a dermatophyte, A. fulvescens has occasionally been shown to cause onychomycosis infections in humans. Its recognition in the laboratory is clinically important for correct diagnosis and treatment of human dermal infections.

Contents

Taxonomy

Aphanoascus fulvescens has faced many discrepancies and challenges for proper taxonomic placement. The naming and classification of A. fulvescens has been subject to taxonomic confusion since the original discovery of the species. [1] The genus Aphanoascus , to which A. fulvescens belongs, was first described in 1890 by Hugo Zukal after isolating it from alligator dung in Vienna. [1] [2] Zukal named this fungus Aphanoascus cinnabarinus. The same fungus however, had already been isolated earlier in 1875 under the name Badhamia fulvescens by Cooke. The genus Aphanoascus was then further reviewed by Apinis in 1968 who deemed A. fulvescens as the type species. While most mycologists accept this title, others argue that Aphanoascus is a synonym for Anixiopsis, which was the genus name given to a soil isolate described by Hansen as Anixiopsis fulvescens. Later in 1973, further confusion was caused with the introduction of Aphanoascus cinnabarinus as the new type species for the genus Aphanoascus by Udagawa & Takada. In 1980, Benny & Kimbrough recognized Aphanoascus and Anixiopsis as two distinct genera, the former distinguished by reticulate ascospores and the latter by ridged ascospores. Whether the two genera are synonymous remains controversial; many authors continue to accept them as one genus. [1] [3] Initially, A. fulvescens was placed in the family Cephalothecaceae by Apinis, in the Onygenaceae by Malloch & Cain and Currah, in Trichocomaceae by Benny & Kimbrough, and in Amauroascaceae by Arx. [2] Today, most mycologists accept A. fulvescens as the type species of the genus Aphanoascus under the family Onygenaceae. [1] A. fulvescens refers to the sexual state, or teleomorph, of the organism. Chrysosporium keratinophilum is regarded by some mycologists as the asexual state, or anamorph, [4] however others argue that this is only the asexual state of Aphanoascus keratinophilus. [5] Aphanoascus fulvescens, Aphanoascus terreus, Aphanoascus canadensis, Aphanoascus reticulisporus, and Keratinophyton durum or Anixiopsis biplanata are the species that are currently accepted under the genus Aphanoascus. [1]

Appearance

Aphanoascus fulvescens (UAMH 11590) Slide culture incubated at 25degC for 41 days, photographed in phase contrast microscopy. Aphanoascus fulvescens anamorph.jpg
Aphanoascus fulvescens (UAMH 11590) Slide culture incubated at 25°C for 41 days, photographed in phase contrast microscopy.
Aphanoascus fulvescens (UAMH 11590) on cereal agar after 21 days incubation at 25degC. Aphanoascus fulvescens culture.jpg
Aphanoascus fulvescens (UAMH 11590) on cereal agar after 21 days incubation at 25°C.

The colonies of Aphanoascus fulvescens at 30 °C (86 °F) on glucose-peptone agar have a flat topology and a powdery to felt-like texture and are usually white to cream coloured depending on the number of brown ascomata present on the surface. Under the microscope, A. fulvescens is seen to have numerous, large club-shaped conidia with older colonies containing fruiting bodies, or ascomata, at their centres. These fruiting bodies are relatively large, ranging from 290–500  μm in diameter, and are either colourless or have a light brown pigment. [5] The presence of the ascomata is characteristic of all members of the Ascomycota. The ascomata are smooth and have thick, enclosed walls lacking any openings. They reach full maturity after 8–10 days of colonial growth at optimal temperatures and eventually burst to release the asci contained within them. The asci have walls composed of two to four layers of flattened cells which in total amount to 4–6 μm in thickness. There are eight ascospores contained within each ascus in A. fulvescens colonies. The ellipsoidal ascospores are a light brown colour and are either lens shaped or disc shaped. They can be as large as 5 x 3.5 μm and have notably rough walls. The ascospores of A. fulvescens are different than those of other members of the Amauroascaeae which have ascospores that are usually globular and round. Rather, the unicellular ascospores of A. fulvescens are found to be flattened with reticulate walls. The hyphae of A. fulvescens are hyaline, branched, and contain many cross-walls (setpa). They are generally 1.7–3 μm wide and are contained within thin walls. [1]

The colonial appearance of A. fulvescens generally mimics that of species in the genus Trichophyton and Chrysosporium while under the microscope the appearance of the organism resembles that of the genus Aspergillus . The differentiation of A. fulvescens from Aspergillus spp. is based on their conidial states. [5]

Ecology

Aphanoascus fulvescens is commonly found in the soil and in dung, living as a keratinophilic saprotroph. It is also often isolated from keratin-rich tissues such as hair and nails that have been discarded from the host. [6] A. fulvescens is a geophilic fungus and therefore does not normally infect mammals. The organism is more commonly isolated from soil that has been inhabited frequently by animals than soil that has not. However, while this fungus is not a true dermatophyte, it is opportunistic and has been seen to cause dermatophytosis in humans and other mammals on occasion. [2] [7] A. fulvescens has a worldwide distribution, however it is more frequently isolated in temperate climates. This is because the organism has optimal growth at 28 °C at which it grows 3–4 mm per day and up to 25 mm per week. At elevated temperatures, such as that of the human body (37 °C), A. fulvescens shows restricted growth, averaging only 5–6 mm of growth over the course of seven days. [1] This may be a possible explanation as to why infections involving A. fulvescens are uncommon in humans and other mammals.

Pathogenicity

While Aphanoascus fulvescens is a geophilic fungus, it is also opportunistic and therefore has been isolated from humans and animals on occasion. In order to cause infection, the fungus must first adhere to the host cells. In vivo and in vitro experiments have proposed the possible role of secreted serine proteases in order to mediate this adhesion. Adhesion of A. fulvescens to the host cell is necessary, because the organism cannot degrade keratin from a distance and instead uses pressure to penetrate the keratin-rich cells of the host. [8]

Skin

Keratinophilic fungal species that fall under the genus Trichophyton , Epidermophyton , or Microsporum , are pathogenic to humans and other animals, and are referred to as dermatophytes on the basis of their ability to cause dermatophytosis in these hosts. [9] However, infections in these hosts caused by soil-derived keratinophilic saprotrophs like A. fulvescens are very seldom and only a few cases have been documented in the literature. The first documented case of A. fulvescens causing tinea corporis was in 1970 when the fungus was repeatedly isolated from a 4 x 5 cm red patch on the inner right thigh of a 21-year-old white male. This case showcases the clinical importance of non-dermatophyte keratinophilic fungi such as A. fulvescens as a result of the ability to cause dermatophytosis in the form of tinea corporis in humans. While visually, the case of tinea corporis was indistinguishable from those caused by true dermatophytes, the infection did not respond well to typical treatment. This observation is crucial for correct diagnosis and treatment of the skin lesion and highlights the necessity of awareness for atypical opportunistic human pathogenic fungi. [2]

Hair

The cuticle is the first region of the hair that is attacked in an A. fulvescens infection. [10] [11] This attack resembles that of true dermatophytes in that some lateral hyphae give rise to fronded mycelium. However, some hyphae also give rise to appressoria, or flattened hyphal pressing organs, which are characteristic of non-keratinophilic fungi. Dermatophytes digest the hair cuticle rapidly, unlike A. fulvescens, which breaks the cuticle down so slowly that the scales are still visible for weeks after the hair has been infected. [10]

After the cuticle has been broken down, the next structure that is targeted is the medulla. This region is first colonized by hyphae present in the cuticle and fungal growth is more rapid here because the trichohyalin of the medulla is more readily digested than the keratin of the cuticle. The medullary mycelium then grow back towards the cuticle in a manner that makes the origin of the mycelium undetectable after 5–6 days of infection. [11]

The cortex is the third, and last region of the hair to be attacked by A. fulvescens. Appressoria penetrate through to the cortex to produce cells of various sizes, giving the cortex a swollen morphology. This swollen mass of cells can proliferate in all directions to give rise to a large mass of mycelium that protrudes backwards out of the hair. [11] Dermatophytes are seen to behave in a similar manner, however, instead of a bulging mass, the mycelium grows in a more organized fashion, as a single collapsed column. [9]

Growth of the cortical mycelium can be at any angle to the hair in an attack from A. fulvescens, while true dermatophytes have the characteristic of growing along the hair in parallel. [11] A. fulvescens can attack at any point along the hair and often causes a marked swelling upon entry sites. The mycelium penetrates the hair by exerting a high amount of pressure on the hair cells and is always closely pressed to the cavity walls. A. fulvescens cannot digest keratin from a distance, as seen in dermatophytes, but rather seems to require direct contact with the keratin-rich substrate. [8] The digestion of keratin by A. fulvescens happens in two stages, the first of which involves the denaturation of keratin. The second stage involves the actual digestion of keratin by A. fulvescens, which then grows into the remaining space. [8] [10] An infected hair is completely replaced by the mycelium of A. fulvescens within 6–8 weeks. [11]

Treatment

Topical steroids and antibiotic ointments such as Neosporin have not only shown to be ineffective in treating dermatophytosis caused by Aphanoascus fulvescens, but have also been shown to enhance its fungal growth. Ringworm infections caused by A. fulvescens in animals have been successfully treated with anti-fungal drugs such as Tinactin, which contains tolnaftate as its active ingredient, and Grisactin, which contains griseofulvin as its active ingredient. However, topical treatment of human A. fulvescens infections with tolnaftate-containing drugs has been shown to worsen the lesions, causing further inflammation and increased sensitivity. Treatment with griseofulvin has proven somewhat effective in reducing lesion sizes and appears to have a dose-dependent effect. While lesions continue to heal after increased griseofulvin administration, there is some residual scarring of the infected area. [2] Currently, there is no documentation providing evidence of an anti-fungal treatment that is completely effective against human dermatophytosis caused by A. fulvescens.

Related Research Articles

Dermatophyte is a common label for a group of fungus of Arthrodermataceae that commonly causes skin disease in animals and humans. Traditionally, these anamorphic mold genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota. As of 2019 a total of nine genera are identified and new phylogenetic taxonomy has been proposed.

<span class="mw-page-title-main">Tinea capitis</span> Cutaneous fungal infection of the scalp

Tinea capitis is a cutaneous fungal infection (dermatophytosis) of the scalp. The disease is primarily caused by dermatophytes in the genera Trichophyton and Microsporum that invade the hair shaft. The clinical presentation is typically single or multiple patches of hair loss, sometimes with a 'black dot' pattern, that may be accompanied by inflammation, scaling, pustules, and itching. Uncommon in adults, tinea capitis is predominantly seen in pre-pubertal children, more often boys than girls.

<span class="mw-page-title-main">Dermatophytosis</span> Fungal infection of the skin

Dermatophytosis, also known as ringworm, is a fungal infection of the skin. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the area affected. Symptoms begin four to fourteen days after exposure. Multiple areas can be affected at a given time.

<i>Trichophyton rubrum</i> Species of fungus

Trichophyton rubrum is a dermatophytic fungus in the phylum Ascomycota. It is an exclusively clonal, anthropophilic saprotroph that colonizes the upper layers of dead skin, and is the most common cause of athlete's foot, fungal infection of nail, jock itch, and ringworm worldwide. Trichophyton rubrum was first described by Malmsten in 1845 and is currently considered to be a complex of species that comprises multiple, geographically patterned morphotypes, several of which have been formally described as distinct taxa, including T. raubitschekii, T. gourvilii, T. megninii and T. soudanense.

<i>Piedraia hortae</i> Species of fungus

Piedraia hortae is a superficial fungus that exists in the soils of tropical and subtropical environments and affects both sexes of all ages. The fungus grows very slowly, forming dark hyphae, which contain chlamydoconidia cells and black colonies when grown on agar. Piedraia hortae is a dermatophyte and causes a superficial fungal infection known as black piedra, which causes the formation of black nodules on the hair shaft and leads to progressive weakening of the hair. The infection usually infects hairs on the scalp and beard, but other varieties tend to grow on pubic hairs. The infection is usually treated with cutting or shaving of the hair and followed by the application of anti-fungal and topical agents. The fungus is used for cosmetic purposes to darken hair in some societies as a symbol of attractiveness.

<span class="mw-page-title-main">Fungal folliculitis</span> Inflammation of hair follicles due to fungal infection

Majocchi's granuloma is a skin condition characterized by deep, pustular plaques, and is a form of tinea corporis. It is a localized form of fungal folliculitis. Lesions often have a pink and scaly central component with pustules or folliculocentric papules at the periphery. The name comes from Domenico Majocchi, who discovered the disorder in 1883. Majocchi was a professor of dermatology at the University of Parma and later the University of Bologna. The most common dermatophyte is called Trichophyton rubrum.

<i>Microsporum gypseum</i> Species of fungus

Microsporum gypseum is a soil-associated dermatophyte that occasionally is known to colonise and infect the upper dead layers of the skin of mammals. The name refers to an asexual "form-taxon" that has been associated with four related biological species of fungi: the pathogenic taxa Arthroderma incurvatum, A. gypsea, A. fulva and the non-pathogenic saprotroph A. corniculata. More recent studies have restricted M. gypseum to two teleomorphic species A. gypseum and A. incurvatum. The conidial states of A. fulva and A. corniculata have been assigned to M. fulvum and M. boullardii. Because the anamorphic states of these fungi are so similar, they can be identified reliably only by mating. Two mating strains have been discovered, "+" and "–". The classification of this species has been based on the characteristically rough-walled, blunt, club-shaped, multicelled macroconidia. Synonyms include Achorion gypseum, Microsporum flavescens, M. scorteum, and M. xanthodes. There has been past nomenclatural confusion in the usage of the generic names Microsporum and Microsporon.

Trichophyton concentricum is an anthropophilic dermatophyte believed to be an etiological agent of a type of skin mycosis in humans, evidenced by scaly cutaneous patches on the body known as tinea imbricata. This fungus has been found mainly in the Pacific Islands and South America.

Microsporum nanum is a pathogenic fungus in the family Arthrodermataceae. It is a type of dermatophyte that causes infection in dead keratinized tissues such as skin, hair, and nails. Microsporum nanum is found worldwide and is both zoophilic and geophilic. Animals such as pigs and sheep are the natural hosts for the fungus; however, infection of humans is also possible. Majority of the human cases reported are associated with pig farming. The fungus can invade the skin of the host; if it is scratched off by the infected animal, the fungus is still capable of reproducing in soil.

Nannizziopsis vreisii is a keratinophilic microfungus in the Family Onygenaceae of the order Onygenales. Also included in this family are dematophytes and saprophytic species. While the ecology of N. vriessi is not well known, there has been several studies which identifies the Chrysosporium anamorph of N. vriesii as a causal agent of skin lesions in reptiles across several regions. This species is usually identified under a microscope by its white ascomata, and hyaline and globose ascospores. Like many other fungi, N. vreisii has a sexual and asexual state, the asexual states are classified as the genus Chryososporium, Malbranchea or Sporendonema.

<i>Chrysosporium keratinophilum</i> Species of fungus

Chrysosporium keratinophilum is a mold that is closely related to the dermatophytic fungi and is mainly found in soil and the coats of wild animals to break down keratin. Chrysosporium keratinophilum is one of the more commonly occurring species of the genus Chrysosporium in nature. It is easily detected due to its characteristic "light-bulb" shape and flat base. Chrysosporium keratinophilum is most commonly found in keratin-rich, dead materials such as feathers, skin scales, hair, and hooves. Although not identified as pathogenic, it is a regular contaminant of cutaneous specimens which leads to the common misinterpretation that this fungus is pathogenic.

<i>Chaetomium globosum</i> Species of fungus

Chaetomium globosum is a well-known mesophilic member of the mold family Chaetomiaceae. It is a saprophytic fungus that primarily resides on plants, soil, straw, and dung. Endophytic C. globosum assists in cellulose decomposition of plant cells. They are found in habitats ranging from forest plants to mountain soils across various biomes. C. globosum colonies can also be found indoors and on wooden products.

Thielavia subthermophila is a ubiquitous, filamentous fungus that is a member of the phylum Ascomycota and order Sordariales. Known to be found on plants of arid environments, it is an endophyte with thermophilic properties, and possesses dense, pigmented mycelium. Thielavia subthermophila has rarely been identified as a human pathogen, with a small number of clinical cases including ocular and brain infections. For treatment, antifungal drugs such as amphotericin B have been used topically or intravenously, depending upon the condition.

Amauroascus kuehnii is a fungus in the phylum Ascomycota, class Eurotiomycetes. It is keratinophilic but not known to cause any human disease. It has been isolated from animal dungs, soil, and keratinous surfaces of live or deceased animals.

<i>Epidermophyton floccosum</i> Species of fungus

Epidermophyton floccosum is a filamentous fungus that causes skin and nail infections in humans. This anthropophilic dermatophyte can lead to diseases such as tinea pedis, tinea cruris, tinea corporis and onychomycosis. Diagnostic approaches of the fungal infection include physical examination, culture testing, and molecular detection. Topical antifungal treatment, such as the use of terbinafine, itraconazole, voriconazole, and ketoconazole, is often effective.

<i>Keratinophyton durum</i> Species of fungus

Keratinophyton durum is a keratinophilic fungus, that grows on keratin found in decomposing or shed animal hair and bird feathers. Various studies conducted in Canada, Japan, India, Spain, Poland, Ivory Coast and Iraq have isolated this fungus from decomposing animal hair and bird feathers using SDA and hair-bait technique. Presence of fungus in soil sediments and their ability to decompose hairs make them a potential human pathogen.

<i>Ctenomyces serratus</i> Species of fungus

Ctenomyces serratus is a keratinophilic fungal soil saprotroph classified by the German mycologist, Michael Emil Eduard Eidam in 1880, who found it growing on an old decayed feather. Many accounts have shown that it has a global distribution, having been isolated in select soils as well as on feathers and other substrates with high keratin content. It has also been found in indoor dust of hospitals and houses in Kanpur, Northern India and as a common keratinophilic soil fungus in urban Berlin. This species has been associated with nail infections in humans as well as skin lesions and slower hair growth in guinea pigs.

Microascus manginii is a filamentous fungal species in the genus Microascus. It produces both sexual (teleomorph) and asexual (anamorph) reproductive stages known as M. manginii and Scopulariopsis candida, respectively. Several synonyms appear in the literature because of taxonomic revisions and re-isolation of the species by different researchers. M. manginii is saprotrophic and commonly inhabits soil, indoor environments and decaying plant material. It is distinguishable from closely related species by its light colored and heart-shaped ascospores used for sexual reproduction. Scopulariopsis candida has been identified as the cause of some invasive infections, often in immunocompromised hosts, but is not considered a common human pathogen. There is concern about amphotericin B resistance in S. candida.

Myriodontium keratinophilum is a fungus widespread in nature, most abundantly found in keratin-rich environments such as feathers, nails and hair. Despite its ability to colonize keratinous surfaces of human body, the species has been known to be non-pathogenic in man and is phylogentically distant to other human pathogenic species, such as anthropophilic dermatophytes. However, its occasional isolation from clinical specimens along with its keratinolytic properties suggest the possibility it may contribute to disease.

Microsporum fulvum is a wildly-distributed dermatophyte species in the Fungi Kingdom. It is known to be a close relative to other dermatophytes such as Trichophyton andEpidermophyton. The fungus is common within soil environments and grows well on keratinized material, such as hair, nails and dead skin. It is recognized as an opportunistic fungal pathogen capable of causing cutaneous mycoses in humans and animals. Originally, the fungus was thought to be Microsporum gypseum until enhanced genetic examination separated the two as distinct species in 1963.

References

  1. 1 2 3 4 5 6 7 Cano J, Guarro J. (April 1990). “The genus Aphanoascus”. Mycological Research94: 355–377
  2. 1 2 3 4 5 Rippon JW, Lee FC, McMillen S. (1970). “Dermatophyte infection caused by Aphanoascus fulvescens”. Archives of Dermatology102(5):552-&. doi:10.1001/archderm.102.5.552
  3. ↑ Jong SC, Davis EE (1975). “The imperfect state of Aphanoascus”. Mycologia67:1143–7
  4. ↑ “Synonym and Classification Data for Aphanoascus spp.” Doctor Fungus. 2007. Retrieved on 11/02/13. "Archived copy". Archived from the original on 2013-10-19. Retrieved 2013-10-17.{{cite web}}: CS1 maint: archived copy as title (link)
  5. 1 2 3 Campbell, C. K., Johnson, E. M. and Warnock, D. W. (2013) "Miscellaneous Moulds".Identification of Pathogenic Fungi Second Edition. Wiley-Blackwell. Oxford, UK. ISBN   9781444330700
  6. ↑ Cano J, Sagues M, Barrio E, Vidal P, Castaneda RF, Gene J, Guarro J(December 2002). “Molecular taxonomy of Aphanoascus and description of two new species from soil”. Studies in Mycology1(47):153–164
  7. ↑ Marin G, Campos R. (1984). “Dermatophytosis due to Aphanoascus fulvescens”. Sabouraudia Journal of Medical and Veterinary Mycology22(4):311–14.
  8. 1 2 3 Cano J, Guarro J, Mayayo J. (January 1990). “Experimental Pathogenicity of Aphanoascus spp.”. Mycoses33(1): 41–45.
  9. 1 2 de Vries G. (1962). “Keratinophilic fungi and their action”. Antonie van Leeuwenhoek28:121–33
  10. 1 2 3 English MP. “Destruction of hair by Chrysosporium keratinophilum”. (April 1969). Transactions of the British Mycological Society52(2):247–255.
  11. 1 2 3 4 5 Cano J. Guarro J, Figueras M. (March 1991). "Study of the invasion of human hair in vitro by Aphanoascus spp." Mycoses. 34(3):145–152.
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