Aspergillus flavus: Introduction, Pathogenecity, Laboratory Diagnosis and Treatment
Introduction of Aspergillus flavus
Aspergillus flavus on Czapek- Dox agar after cultivation of clinical specimen
Colonial characteristics- granular flat, often with radial grooves, initially yellow but quickly becoming bright to dark yellow-green with age. This picture of A. flavus is due to 5 days of incubation at room temperature i.e. 25°C. A. flavus is one of the most common and easily identifiable species of the genus Aspergillus, initially yellow but quickly becoming bright to dark yellow-green with age. This species is very commonly found in aspergillomas and is the most frequently encountered agent of otomycosis. It is also a common laboratory contaminant and comes under risk group (RG)-1 organism.
Pathogenicity of Aspergillus flavus
Aspergillosis: It is a granulomatous, narcotizing, and cavity disease of the lung. often with hematogenous spread to other organs.
Manifestation
- Otomycosis and keratitis
- Toxicity from ingestion of fungal contaminated foods.
- Allergic manifestation
- Colonization of fungus in the various body cavities and debilitated tissues
- The invasive granulomatous disease of the lung with inflammation and necrosis
- The systemic disseminated disease that is usually fatal if not treated-
- increased incidence has been seen in
- Leukemia
- Diabetic patient
- AIDS
- Renal transplantation
- Cardiac transplantation
Laboratory Diagnosis of Aspergillus flavus
Specimens: Samples depend on the site of infection and some common specimens are –
- Sputum
- sinus drainage
- Bronchial washing
- Ear discharge
Direct smear examination
- Wet mount preparation: 20% Potassium Hydroxide (KOH) preparation
- Gram stain
- Grocott’s Methenamine silver stain
- PAS stain
- Acridine orange
Culture
One at 37°C and another 25°C if necessary for up to 28 days.
Note: Culture correlation with direct smear examination is important because Aspergillus species are common laboratory contaminants.
Six consecutive morning samples are required out of which should show the same fungal growth in 50% sample.
Colony characteristic
- Velvety texture
- mold type growth
- pigmentation- yellow
Morphology
- Lacto phenol cotton blue (LPCB) preparation
- Conidiophore length: 1.5-3.0 mm
- Vesicle width: 45-75 μm
- Phialides: Biseriate
- Color of conidia: yellow
- Diameter of conidia: 4.5-5.0 μm
Other methods
- Skin test
- Agar gel diffusion
Treatment
Following drugs are used to treat this etiological agent-
- Amphotericin B
- Itraconazole
- Voriconazole
- Posaconazole
- Anidulafungin
- Caspofungin
Further Readings
- A Textbook of Medical Mycology. Editor: Jagdish Chander. Publication Mehata, India.
- Medical Mycology. Editors: Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
- Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
- Description of Medical fungi, David Ellis, Stephen Davis, Helen Alexiou, Rosemary Handke, Robyn Bartley, Second edition