Exophiala pisciphila

Updated : November 15, 2023

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Exophiala pisciphila is a black yeast-like fungus that tends to cause infections in humans and animals. It is frequently encountered in aquatic environments, including fish tanks, ponds, and pools. Additionally, this fungus can thrive on damp surfaces like shower curtains, sinks, and faucets. Notably, Exophiala pisciphila is commonly distributed in soil, plants, and water, with a documented presence in regions such as North America, the Netherlands, the United Kingdom, and Australia.  

The exact incidence and prevalence of Exophiala pisciphila infections in human populations remain largely unknown. Nonetheless, sporadic case reports have emerged from diverse countries, underscoring its potential to affect individuals in various geographic locations, including China, Iran, Italy, Japan, Spain, and the United States.  

The history of Exophiala pisciphila’s recognition in medical mycology dates back to the late 1960s when a systemic mycosis outbreak was identified in channel catfish from an Alabama pond. This marked the initial characterization of the fungus as Exophiala by Nikola Fijan in 1969. Subsequently, in 1974, Michael McGinnis and Libero Ajello conducted a reevaluation, contributing to our understanding of this fungal pathogen.

Notably, one case of human disease linked to E. pisciphila was reported in Brazil, involving a liver transplant recipient undergoing immunosuppressive therapy who developed a skin infection. Fortunately, the infection did not disseminate in this instance and was successfully resolved with therapy within a month. 

 

Classification and Structure: 

Kingdom: Fungi 

Phylum: Ascomycota 

Class: Eurotiomycetes 

Order: Chaetothyriales 

Family: Herpotrichiellaceae 

Genus: Exophiala 

Species: E. pisciphila  

Exophiala pisciphila forms branching filaments called hyphae, which compose the mycelium or the fungal body. These hyphae are septate, possessing cross-walls that segment them into distinct units. They typically range from 1 to 3 µm in diameter and feature smooth or slightly roughened surfaces.  

This fungus generates asexual spores known as conidia, exhibiting polymorphism with various shapes, including oval, cylindrical, clavate, fusiform, and irregular. Conidia typically measure 2–6 µm in length and 1–3 µm in width.  

Colonies of Exophiala pisciphila are characterized by slow growth and typically reach diameters of 20 to 35 millimeters after two weeks of incubation at 25 °C. This growth pattern defines the fungal structure and its development. 

 

Exophiala pisciphila, a black yeast-like fungus, possesses various distinctive features. Its cell wall displays various antigens, including mannans, glucans, and melanin, contributing to its resilience and adaptability in harsh environments. Notably, this fungus exhibits a remarkable tolerance to metal ions, enabling it to thrive even in heavily polluted soils with elevated metal concentrations.  

Furthermore, E. pisciphila has been a source of valuable secondary metabolites. Exophilin A, one such metabolite, has been identified as a novel antibiotic effective against Gram-positive bacteria. Additionally, this species produces a newly discovered polyketide compound, 1-(3,5-dihydroxyphenyl)-4-hydroxypentan-2-one, which may possess antimicrobial properties.

Another significant discovery is Exophilic acid, a novel fungal metabolite known to inhibit HIV-1 integrase, a critical enzyme for the replication and spread of HIV. This finding underscores its potential utility in antiretroviral therapy. One particular strain of Exophiala pisciphila, denoted as H93, was isolated from soil heavily contaminated with metal ions in China.  

Exophiala pisciphila‘s pathogenesis involves several transmission modes and subsequent infections in humans. Traumatic implantation is a shared entry route, primarily through wounds or injuries caused by fish spines or scales.

This mode often leads to subcutaneous infections characterized by the formation of nodules, abscesses, ulcers, and granulomas in the skin and subcutaneous tissues, resembling conditions such as chromoblastomycosis or phaeohyphomycosis.  

Another means of transmission is inhaling contaminated dust or water droplets, which can result in pulmonary or systemic infections. This respiratory route may lead to more severe and disseminated infections, particularly in immunocompromised or immunosuppressed individuals.   

Furthermore, the fungus can be transmitted from infected fish or amphibians to humans through direct contact or ingestion. This highlights the versatility of Exophiala pisciphila in causing a range of infections, from localized subcutaneous lesions to more severe and widespread conditions, particularly when the host’s immune system is compromised. 

The immune system deploys specialized cells to combat fungal infections. Neutrophils, monocytes, macrophages, and certain lymphocytes are vital in recognizing and neutralizing Exophiala pisciphila. These cells possess receptors for specific complement fragments, enabling them to effectively recognize and engage with the fungus.  

The complement system, a part of the immune response, plays a role in identifying and opsonizing Exophiala pisciphila. This helps phagocytic cells, such as macrophages, recognize and ingest the fungus. Complement activation can also generate chemoattractants, such as C5a, which recruit inflammatory cells to the site of infection.  

Cell-mediated immunity is another vital component of the defense against fungal infections. This immune response involves antigen-presenting cells, T lymphocytes, and the release of cytokines that activate effector cells to inhibit or kill the fungal pathogen. Impairment of CMI, as seen in conditions like AIDS, lymphomas, and immunosuppressive medication use, can predispose individuals to fungal infections by reducing their ability to mount an effective immune response. 

 

Clinical manifestations of Exophiala pisciphila infections can encompass a range of conditions:  

Allergic Bronchopulmonary Mycosis (ABPM):E. pisciphila can trigger hypersensitivity reactions in the airways, leading to symptoms akin to asthma. Patients may experience coughing, fever, weight loss, and hemoptysis.  

Cutaneous Infection: Cutaneous infections by E. pisciphila can manifest as skin lesions, which may present as papules, pustules, ulcers, or verrucous growths. Satellite lesions often surround these lesions and can resemble other skin conditions like chromoblastomycosis or phaeohyphomycosis under histological examination.  

Mycetoma:Exophiala pisciphila can cause chronic granulomatous infections that primarily affect the subcutaneous tissue and bone, most commonly in the feet or hands. This infection can drain sinuses and form grain-like structures containing the fungus.  

Subcutaneous Cyst: A less common form of Exophiala pisciphila infection involves the development of cystic lesions under the skin, typically on the face or neck. These cysts contain fungal elements and inflammatory cells.  

Endocarditis:Exophiala pisciphila can infect the heart valves, leading to fever, heart murmurs, embolic complications, and even heart failure. Diagnosis often requires blood culture or histopathology of the valve tissue.  

Cerebral and Disseminated Infection:E. pisciphila infections can become severe and potentially fatal in immunocompromised individuals. This infection affects the brain and other organs, causing symptoms like headaches, seizures, focal neurological deficits, meningitis, abscesses, or infarcts. 

 

Diagnosing Exophiala pisciphila infections in humans involves a multifaceted approach, considering clinical presentation, histopathology, and fungal culture from affected tissues or fluids. Several diagnostic tests are utilized in this process:  

KOH Mount: A quick and straightforward test entails adding a drop of potassium hydroxide (KOH) to a sample of tissue or fluid and examining it under a microscope. The KOH dissolves cellular material, revealing fungal elements, which appear as brown septate branching hyphae or dark brown budding cells.  

Culture test: This test involves inoculating a tissue or fluid sample onto a suitable growth medium, like potato dextrose agar, and incubating it at 25°C for two weeks. Exophiala pisciphila typically forms slow-growing colonies that are gray to green-black on the upper surface and black on the reverse surface, with a dry and fluffy texture due to aerial hyphae formation.  

Histopathology: This involves taking a biopsy of the infected tissue and staining it with specialized stains, such as Fontana-Masson or Gomori methenamine silver. This staining reveals pigmented hyphae and conidia produced by the fungus, visible as dark brown structures within the tissue.  

Molecular Methods: These tests focus on extracting the fungus’s DNA from the tissue or fluid sample and amplifying it using polymerase chain reaction (PCR) with specific primers. The amplified DNA is detected by reverse line blot (RLB) hybridization, loop-mediated isothermal amplification (LAMP), or sequencing. These molecular techniques offer rapid and precise species-level identification of Exophiala pisciphila. 

 

  • Regularly clean and disinfect aquariums, decorative items, stones, and food items that could be sources of the fungus. Effective agents like chlorine, formalin, or other suitable disinfectants can eliminate the fungus. 
  • Refrain from direct contact with fish and amphibians that the fungus may infect. Only consume or touch them while observing proper hygiene practices. 
  • Steer clear of environments with potential fungal contamination, such as soil, water, or aquariums. This reduces the risk of exposure to Exophiala pisciphila. Utilize gloves, boots, and protective clothing when handling these materials. 
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Exophiala pisciphila

Updated : November 15, 2023

Mail Whatsapp PDF Image



Exophiala pisciphila is a black yeast-like fungus that tends to cause infections in humans and animals. It is frequently encountered in aquatic environments, including fish tanks, ponds, and pools. Additionally, this fungus can thrive on damp surfaces like shower curtains, sinks, and faucets. Notably, Exophiala pisciphila is commonly distributed in soil, plants, and water, with a documented presence in regions such as North America, the Netherlands, the United Kingdom, and Australia.  

The exact incidence and prevalence of Exophiala pisciphila infections in human populations remain largely unknown. Nonetheless, sporadic case reports have emerged from diverse countries, underscoring its potential to affect individuals in various geographic locations, including China, Iran, Italy, Japan, Spain, and the United States.  

The history of Exophiala pisciphila’s recognition in medical mycology dates back to the late 1960s when a systemic mycosis outbreak was identified in channel catfish from an Alabama pond. This marked the initial characterization of the fungus as Exophiala by Nikola Fijan in 1969. Subsequently, in 1974, Michael McGinnis and Libero Ajello conducted a reevaluation, contributing to our understanding of this fungal pathogen.

Notably, one case of human disease linked to E. pisciphila was reported in Brazil, involving a liver transplant recipient undergoing immunosuppressive therapy who developed a skin infection. Fortunately, the infection did not disseminate in this instance and was successfully resolved with therapy within a month. 

 

Classification and Structure: 

Kingdom: Fungi 

Phylum: Ascomycota 

Class: Eurotiomycetes 

Order: Chaetothyriales 

Family: Herpotrichiellaceae 

Genus: Exophiala 

Species: E. pisciphila  

Exophiala pisciphila forms branching filaments called hyphae, which compose the mycelium or the fungal body. These hyphae are septate, possessing cross-walls that segment them into distinct units. They typically range from 1 to 3 µm in diameter and feature smooth or slightly roughened surfaces.  

This fungus generates asexual spores known as conidia, exhibiting polymorphism with various shapes, including oval, cylindrical, clavate, fusiform, and irregular. Conidia typically measure 2–6 µm in length and 1–3 µm in width.  

Colonies of Exophiala pisciphila are characterized by slow growth and typically reach diameters of 20 to 35 millimeters after two weeks of incubation at 25 °C. This growth pattern defines the fungal structure and its development. 

 

Exophiala pisciphila, a black yeast-like fungus, possesses various distinctive features. Its cell wall displays various antigens, including mannans, glucans, and melanin, contributing to its resilience and adaptability in harsh environments. Notably, this fungus exhibits a remarkable tolerance to metal ions, enabling it to thrive even in heavily polluted soils with elevated metal concentrations.  

Furthermore, E. pisciphila has been a source of valuable secondary metabolites. Exophilin A, one such metabolite, has been identified as a novel antibiotic effective against Gram-positive bacteria. Additionally, this species produces a newly discovered polyketide compound, 1-(3,5-dihydroxyphenyl)-4-hydroxypentan-2-one, which may possess antimicrobial properties.

Another significant discovery is Exophilic acid, a novel fungal metabolite known to inhibit HIV-1 integrase, a critical enzyme for the replication and spread of HIV. This finding underscores its potential utility in antiretroviral therapy. One particular strain of Exophiala pisciphila, denoted as H93, was isolated from soil heavily contaminated with metal ions in China.  

Exophiala pisciphila‘s pathogenesis involves several transmission modes and subsequent infections in humans. Traumatic implantation is a shared entry route, primarily through wounds or injuries caused by fish spines or scales.

This mode often leads to subcutaneous infections characterized by the formation of nodules, abscesses, ulcers, and granulomas in the skin and subcutaneous tissues, resembling conditions such as chromoblastomycosis or phaeohyphomycosis.  

Another means of transmission is inhaling contaminated dust or water droplets, which can result in pulmonary or systemic infections. This respiratory route may lead to more severe and disseminated infections, particularly in immunocompromised or immunosuppressed individuals.   

Furthermore, the fungus can be transmitted from infected fish or amphibians to humans through direct contact or ingestion. This highlights the versatility of Exophiala pisciphila in causing a range of infections, from localized subcutaneous lesions to more severe and widespread conditions, particularly when the host’s immune system is compromised. 

The immune system deploys specialized cells to combat fungal infections. Neutrophils, monocytes, macrophages, and certain lymphocytes are vital in recognizing and neutralizing Exophiala pisciphila. These cells possess receptors for specific complement fragments, enabling them to effectively recognize and engage with the fungus.  

The complement system, a part of the immune response, plays a role in identifying and opsonizing Exophiala pisciphila. This helps phagocytic cells, such as macrophages, recognize and ingest the fungus. Complement activation can also generate chemoattractants, such as C5a, which recruit inflammatory cells to the site of infection.  

Cell-mediated immunity is another vital component of the defense against fungal infections. This immune response involves antigen-presenting cells, T lymphocytes, and the release of cytokines that activate effector cells to inhibit or kill the fungal pathogen. Impairment of CMI, as seen in conditions like AIDS, lymphomas, and immunosuppressive medication use, can predispose individuals to fungal infections by reducing their ability to mount an effective immune response. 

 

Clinical manifestations of Exophiala pisciphila infections can encompass a range of conditions:  

Allergic Bronchopulmonary Mycosis (ABPM):E. pisciphila can trigger hypersensitivity reactions in the airways, leading to symptoms akin to asthma. Patients may experience coughing, fever, weight loss, and hemoptysis.  

Cutaneous Infection: Cutaneous infections by E. pisciphila can manifest as skin lesions, which may present as papules, pustules, ulcers, or verrucous growths. Satellite lesions often surround these lesions and can resemble other skin conditions like chromoblastomycosis or phaeohyphomycosis under histological examination.  

Mycetoma:Exophiala pisciphila can cause chronic granulomatous infections that primarily affect the subcutaneous tissue and bone, most commonly in the feet or hands. This infection can drain sinuses and form grain-like structures containing the fungus.  

Subcutaneous Cyst: A less common form of Exophiala pisciphila infection involves the development of cystic lesions under the skin, typically on the face or neck. These cysts contain fungal elements and inflammatory cells.  

Endocarditis:Exophiala pisciphila can infect the heart valves, leading to fever, heart murmurs, embolic complications, and even heart failure. Diagnosis often requires blood culture or histopathology of the valve tissue.  

Cerebral and Disseminated Infection:E. pisciphila infections can become severe and potentially fatal in immunocompromised individuals. This infection affects the brain and other organs, causing symptoms like headaches, seizures, focal neurological deficits, meningitis, abscesses, or infarcts. 

 

Diagnosing Exophiala pisciphila infections in humans involves a multifaceted approach, considering clinical presentation, histopathology, and fungal culture from affected tissues or fluids. Several diagnostic tests are utilized in this process:  

KOH Mount: A quick and straightforward test entails adding a drop of potassium hydroxide (KOH) to a sample of tissue or fluid and examining it under a microscope. The KOH dissolves cellular material, revealing fungal elements, which appear as brown septate branching hyphae or dark brown budding cells.  

Culture test: This test involves inoculating a tissue or fluid sample onto a suitable growth medium, like potato dextrose agar, and incubating it at 25°C for two weeks. Exophiala pisciphila typically forms slow-growing colonies that are gray to green-black on the upper surface and black on the reverse surface, with a dry and fluffy texture due to aerial hyphae formation.  

Histopathology: This involves taking a biopsy of the infected tissue and staining it with specialized stains, such as Fontana-Masson or Gomori methenamine silver. This staining reveals pigmented hyphae and conidia produced by the fungus, visible as dark brown structures within the tissue.  

Molecular Methods: These tests focus on extracting the fungus’s DNA from the tissue or fluid sample and amplifying it using polymerase chain reaction (PCR) with specific primers. The amplified DNA is detected by reverse line blot (RLB) hybridization, loop-mediated isothermal amplification (LAMP), or sequencing. These molecular techniques offer rapid and precise species-level identification of Exophiala pisciphila. 

 

  • Regularly clean and disinfect aquariums, decorative items, stones, and food items that could be sources of the fungus. Effective agents like chlorine, formalin, or other suitable disinfectants can eliminate the fungus. 
  • Refrain from direct contact with fish and amphibians that the fungus may infect. Only consume or touch them while observing proper hygiene practices. 
  • Steer clear of environments with potential fungal contamination, such as soil, water, or aquariums. This reduces the risk of exposure to Exophiala pisciphila. Utilize gloves, boots, and protective clothing when handling these materials. 

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