Exophiala hongkongensis

Last updated

Exophiala hongkongensis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Eurotiomycetes
Order: Chaetothyriales
Family: Herpotrichiellaceae
Genus: Exophiala
Species:
E. hongkongensis
Binomial name
Exophiala hongkongensis
Woo, Ngan, Tsang, Ling, Chan, Leung, Yuen, Lau (2013)

Exophiala hongkongensis is an ascomycete fungus species. Described as new to science in 2013, it was discovered on the toenail clipping of a patient with the fungal disease onychomycosis.

Contents

Taxonomy

The fungus strain, originally named HKU32T, was isolated from a toenail clipping of a 68-year-old female patient with onychomycosis at the Queen Mary Hospital in Hong Kong. The overall morphology of the fungus aligned it with Exophiala , but it had phenotypic characteristics that were not consistent with any other species of that genus. Molecular analysis of four independent DNA regions (ITS, Rpb1, beta-tubulin, and beta-actin) confirmed that it was a new species. It is most closely related to Exophiala nishimurae , with which it forms a clade that is sister to the species E. xenobiotica . [1]

Description

When grown on Sabouraud dextrose agar culture media, the fungus grows slowly as black, slimy, yeast-like colonies that reach a diameter of 2 mm after 14 days at 25 °C (77 °F). Then the colony centers develop a velvety texture and become greenish-gray and dome-shaped, while retaining a slimy and yeast-like margin. After 14 days, the ellipsoidal yeast-like cells are brown when stained with lactophenol cotton blue, and measure 6 by 3.5  μm. They have ringed zones that pinch off to create budding cells. The mycelia of the fungus are swollen and form torulose hyphae (swollen and constricted at intervals) that are pinched at their ends. When the colonies become velvety, the mycelia are not swollen, and conidia are formed in clusters. The average length of the conidiophores is about 10 μm. The conidia are oval to roughly spherical, and typically measure 3 by 2 μm. [1]

Pathogenesis

Exophiala hongkongensis is known only from Hong Kong. Known cases of onychomycosis caused by Exophiala are rare, although this genus commonly causes related skin infections such as phaeohyphomycosis, chromoblastomycosis, and eumycetoma. Previous instances of onychomycosis had been previously traced to E. dermatiditis and E. jeanselmei . In addition to Exophiala hongkongensis, Woo and colleagues identified additional cases caused by E. oligosperma and E. bergeri . All known cases are associated with an underlying disease that causes an immunosuppressive state; in the case of E. hongkonensis, the patient had hypertension. [1]

Related Research Articles

<i>Talaromyces marneffei</i> Species of fungus

Talaromyces marneffei, formerly called Penicillium marneffei, was identified in 1956. The organism is endemic to southeast Asia where it is an important cause of opportunistic infections in those with HIV/AIDS-related immunodeficiency. Incidence of T. marneffei infections has increased due to a rise in HIV infection rates in the region.

<span class="mw-page-title-main">Onychomycosis</span> Medical condition

Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. Symptoms may include white or yellow nail discoloration, thickening of the nail, and separation of the nail from the nail bed. Fingernails may be affected, but it is more common for toenails. Complications may include cellulitis of the lower leg. A number of different types of fungus can cause onychomycosis, including dermatophytes and Fusarium. Risk factors include athlete's foot, other nail diseases, exposure to someone with the condition, peripheral vascular disease, and poor immune function. The diagnosis is generally suspected based on the appearance and confirmed by laboratory testing.

<i>Sporothrix schenckii</i> Species of fungus

Sporothrix schenckii, a fungus that can be found worldwide in the environment, is named for medical student Benjamin Schenck, who in 1896 was the first to isolate it from a human specimen. The species is present in soil as well as in and on living and decomposing plant material such as peat moss. It can infect humans as well as animals and is the causative agent of sporotrichosis, commonly known as "rose handler's disease." The most common route of infection is the introduction of spores to the body through a cut or puncture wound in the skin. Infection commonly occurs in otherwise healthy individuals but is rarely life-threatening and can be treated with antifungals. In the environment it is found growing as filamentous hyphae. In host tissue it is found as a yeast. The transition between the hyphal and yeast forms is temperature dependent making S. schenckii a thermally dimorphic fungus.

<i>Aspergillus terreus</i> Species of fungus

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. This saprotrophic fungus is prevalent in warmer climates such as tropical and subtropical regions. Aside from being located in soil, A. terreus has also been found in habitats such as decomposing vegetation and dust. A. terreus is commonly used in industry to produce important organic acids, such as itaconic acid and cis-aconitic acid, as well as enzymes, like xylanase. It was also the initial source for the drug mevinolin (lovastatin), a drug for lowering serum cholesterol.

Exophiala jeanselmei is a saprotrophic fungus in the family Herpotrichiellaceae. Four varieties have been discovered: Exophiala jeanselmei var. heteromorpha, E. jeanselmei var. lecanii-corni, E. jeanselmei var. jeanselmei, and E. jeanselmei var. castellanii. Other species in the genus Exophiala such as E. dermatitidis and E. spinifera have been reported to have similar annellidic conidiogenesis and may therefore be difficult to differentiate.

<i>Exophiala dermatitidis</i> Species of fungus

Exophiala dermatitidis is a thermophilic black yeast, and a member of the Herpotrichiellaceae. While the species is only found at low abundance in nature, metabolically active strains are commonly isolated in saunas, steam baths, and dish washers. Exophiala dermatitidis only rarely causes infection in humans, however cases have been reported around the world. In East Asia, the species has caused lethal brain infections in young and otherwise healthy individuals. The fungus has been known to cause cutaneous and subcutaneous phaeohyphomycosis, and as a lung colonist in people with cystic fibrosis in Europe. In 2002, an outbreak of systemic E. dermatitidis infection occurred in women who had received contaminated steroid injections at North Carolina hospitals.

Aspergillus sydowii is a pathogenic fungus that causes several diseases in humans. It has been implicated in the death of sea fan corals in the Caribbean Sea.

<i>Aphanoascus fulvescens</i> Species of fungus

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.

<i>Onychocola canadensis</i> Species of fungus

Onychocola canadensis is a relative of the dermatophyte and an occasionally causes onychomycosis. It was described in 1990 from 3 clinical reports in Canada.

Coniochaeta hoffmannii, also known as Lecythophora hoffmannii, is an ascomycete fungus that grows commonly in soil. It has also been categorized as a soft-rot fungus capable of bringing the surface layer of timber into a state of decay, even when safeguarded with preservatives. Additionally, it has pathogenic properties, although it causes serious infection only in rare cases. A plant pathogen lacking a known sexual state, C. hoffmannii has been classified as a "dematiaceous fungus" despite its contradictory lack of pigmentation; both in vivo and in vitro, there is no correlation between its appearance and its classification.

<i>Aspergillus candidus</i> Species of fungus

Aspergillus candidus is a white-spored species of fungus in the genus Aspergillus. Despite its lack of pigmentation, it is closely related to the most darkly-pigmented aspergilli in the Aspergillus niger group. It is a common soil fungus worldwide and is known as a contaminant of a wide array of materials from the indoor environment to foods and products. It is an uncommon agent of onychomycosis and aspergillosis. The species epithet candidus (L.) refers to the white pigmentation of colonies of this fungus. It is from the Candidi section. The fungi in the Candidi section are known for their white spores. It has been isolated from wheat flour, djambee, and wheat grain.

Emmonsia parva is a filamentous, saprotrophic fungus and one of three species within the genus Emmonsia. The fungus is most known for its causal association with the lung disease, adiaspiromycosis which occurs most commonly in small mammals but is also seen in humans. The disease was first described from rodents in Arizona, and the first human case was reported in France in 1964. Since then, the disease has been reported from Honduras, Brazil, the Czech Republic, Russia, the United States of America and Guatemala. Infections in general are quite rare, especially in humans.

<i>Exophiala phaeomuriformis</i> Species of fungus

Exophiala phaeomuriformis is thermophilic fungus belonging to the genus Exophiala and the family Herpotrichiellaceae. it is a member of the group of fungi known as black yeasts, and is typically found in hot and humid locations, such as saunas, bathrooms, and dishwashers. This species can cause skin infections and is typically classified as a Biosafety Risk Group 2 agent.

<i>Cladosporium cladosporioides</i> Species of fungus

Cladosporium cladosporioides is a darkly pigmented mold that occurs world-wide on a wide range of materials both outdoors and indoors. It is one of the most common fungi in outdoor air where its spores are important in seasonal allergic disease. While this species rarely causes invasive disease in animals, it is an important agent of plant disease, attacking both the leaves and fruits of many plants. This species produces asexual spores in delicate, branched chains that break apart readily and drift in the air. It is able to grow under low water conditions and at very low temperatures.

<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.

Exophiala pisciphila is a mesophilic black yeast and member of the dark septate endophytes. This saprotrophic fungus is found commonly in marine and soil environments. It is abundant in harsh environments like soil contaminated with heavy metals. E. pisciphila forms symbiotic relationships with various plants by colonizing on roots, conferring resistance to drought and heavy metal stress. It is an opportunistic pathogen that commonly causes infections in captive fish and amphibians, while rarely causing disease in humans. Secondary metabolites produced by this species have potential clinical antibiotic and antiretroviral applications.

Sarocladium kiliense is a saprobic fungus that is occasionally encountered as a opportunistic pathogen of humans, particularly immunocompromised and individuals. The fungus is frequently found in soil and has been linked with skin and systemic infections. This species is also known to cause disease in the green alga, Cladophora glomerata as well as various fruit and vegetable crops grown in warmer climates.

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.

Cladophialophora arxii is a black yeast shaped dematiaceous fungus that is able to cause serious phaeohyphomycotic infections. C. arxii was first discovered in 1995 in Germany from a 22-year-old female patient suffering multiple granulomatous tracheal tumours. It is a clinical strain that is typically found in humans and is also capable of acting as an opportunistic fungus of other vertebrates Human cases caused by C. arxii have been reported from all parts of the world such as Germany and Australia.

Cephalotheca foveolata is a species of fungus. It is rarely opportunistic and generally manifests as a minor subcutaneous infection.

References

  1. 1 2 3 Woo PC, Ngan AH, Tsang CC, Ling IW, Chan JF, Leung SY, Yuen KY, Lau SK (2013). "Clinical spectrum of Exophiala infections and a novel Exophiala species, Exophiala hongkongensis". Journal of Clinical Microbiology. 51 (1): 260–7. doi:10.1128/JCM.02336-12. PMC   3536265 . PMID   23152554. Open Access logo PLoS transparent.svg