Dematiaceous fungi on SDA: Introduction, Pathogenecity, Laboratory Diagnosis and Treatment
Dematiaceous fungi on SDA
Dematiaceous fungi or another name darkly pigmented filamentous fungi whose morphological characteristics in tissue may contain hyphae, yeast cells, or a combination of these. There is an association of darkly-pigmented hyphomycetes including Alternaria, Exophilia ,Rhinocladiella and so on. Above picture is showing growth of dematiaceous fungi on SDA.
List of dematiaceous fungi/ black fungi
- Alternaria
- Acrophialophora
- Aureobasidium
- Bipolaris
- Chaetomium
- Cladophialophora
- Curvularia
- Exophiala
- Exserohilum
- Fonsecaea
- Hortaea werneckii
- Neoscytalidium dimidiatum
- Ochroconis
- Phaeoacremonium
- Phoma
- Pyrenochaeta
- Rhinocladiella
- Veronaea
Pathogenecity of Dematiaceous fungi
They may cause infection in both immunosuppressed and immunocompetent individuals. Infections may present as chromoblastomycosis, mycetoma, and a spectrum of phaeohyphomycoses varying in severity. The term “phaeohyphomycosis” introduced to determine infections caused by dematiaceous or pigmented filamentous fungi which contain melanin in their cell walls where as Chromoblastomycosis is a chronic fungal infection of the skin and the subcutaneous tissue caused by traumatic inoculation of a specific group of dematiaceous fungi. Mycetoma is a chronic infection of the skin and the subcutaneous tissue which can sometimes also affect muscles, bones, tendons and joints. It is characterised by nodules and sinus tracts that discharge watery fluid or pus containing grains. It of two types -Eumycetoma-causative agent is fungus; Actinomycetoma— causative agent is filamentous bacteria pertaining to order, actinomycetes. Other infections may cause are-
- Keratitis
- Pulmonary infections
- Cerebral infection
- Other localized deep infections: These comprise mainly bone and joint infections and peritonitis.
- Disseminated infection
- Allergic fungal sinusitis and
- Allergic bronchopulmonary mycosis
Mode of Infection
Infection may be through traumatic inoculation, or inhalation with or without dissemination.
Risk factors of Dematiaceous fungal infections
Following are the risk factors of this infection are-
- Hematological malignancies undergoing chemotherapy
- Organ transplantation
- HIV/AIDS and
- Chronic granulomatous disease (CGD)
Laboratory Diagnosis of dematiaceous fungi
Laboratory diagnosis dematiaceous fungi requires sampling at the site of infection; direct microscopy using KOH (potassium hydroxide), haematoxylin and eosin, and/or Fontana-Masson stains; and culturing. Accurate species identification is essential and for this molecular identification requires in which sequencing of ITS and D1/D2 regions of rDNA can be used for molecular identification.
Treatment of dematiaceous fungi
There is no no standardized treatment regimen for black fungal infections but voriconazole, posaconazole, itraconazole and in some cases amphotericin B demonstrate the most consistent in vitro activity against this group of fungi. Oral itraconazole is the drug of choice for most situations. However, voriconazole may have advantages for central nervous system infections because of its ability to achieve good CSF levels, unlike itraconazole. Posaconazole is a broad-spectrum alternative after failure of other antifungal agents. Amphotericin B has been useful in some cases.
Key Notes
- As a result of the large variability in the spectrum of dematiaceous fungi, it is important to obtain in vitro susceptibilities ( AFST) of the individual patient’s fungal isolate although it has not been firmly established that results obtained from susceptibility testing translate into better clinical outcomes.
- A number of species of black fungi are responsible for neurotropic and can cause cerebral abscesses in immunocompetent persons.
- Infections can occur worldwide, but are most common in the tropics, and some species appear to have specific geographic ranges.
- Treatment includes antifungal therapy with or without surgery.
#Dematiaceous fungal growth on SDA and its structures in LPCB preparation as shown below-
#Dematiaceous fungus, Cladosporium growth on SDA and its structures in LPCB preparation as shown below-
References
- Medical Mycology. Editors: Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
- Rippon’s JW: Medical Microbiology. The pathogenic fungi and the pathogenic Actinomycetes. 3rd ed 1988 Publisher WB saunder co, Philadelphia.
- Clinical Microbiology Procedure Hand book , Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
- A Text Book of Medical Mycology. Editor: Jagdish Chandar. Publication Mehata, India.
- Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
- Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
- https://dermnetnz.org/topics/mycetoma
- https://oxfordmedicine.com/view/10.1093/med/9780198755388.001.0001/med-9780198755388-chapter-14
- https://www.sciencedirect.com/science/article/pii/S1198743X14602305