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Cladosporium on SDA: A Dematiaceous Fungus

Cladosporium colonies on SDA as shown above picture as shown above image. Cladosporium species colonies on Sabouraud Dextrose Agar (SDA)  and conidiophores, conidia, and microcyclic conidiogenesis with a secondary ramoconidium forming a conidiophore with a conidium attached in LPCB mount as shown below video-

Keynote- The conidia closest to the conidiophore, and where the chain’s branch, are usually ‘shield-shaped’. The presence of shield-shaped conidia, a distinct hilum, and chains of conidia that are readily disarticulated, are characteristic of this genus as shown in the video clip.

Classification of Cladosporium

Kingdom: Fungi

• Phylum: Ascomycota
• Subphylum: Ascomycotina
• Division: Ascomycota
• Class: Dothideomycetes
• Order: Capnodiales
• Family: Davidiellaceae
• Genus: Cladosporium
• Species: Cladosporium elatums

C. herbarum

C. sphaerospermum

C.  cladosporioides

Note: There are more than 772 species of the genus, Cladosporium but more common species are above mentioned.

Risk Group: Risk group 1 organism

Description and Natural Habitats

Cladosporium species are dematiaceous (pigmented) fungi. They are ubiquitous worldwide indoor and outdoor environments and are commonly isolated from soil and organic matter. They represent the most frequently isolated airborne fungi and also acts as a contaminant on foods.

Morphology of Cladosporium

Macroscopic features: Colonies are slow-growing and growth rate is divided in three groups, rapid grower( 1-5 days), Intermediate grower( 6-12 days) and slow growers ( 13-28 days), mostly olivaceous-brown to blackish-brown but also sometimes grey, buff or brown, suede-like to floccose, often becoming powdery due to the production of abundant conidia. The reverse is olivaceous-black. Vegetative hyphae, conidiophores, and conidia are equally pigmented and thus called dematiaceous (pigmented) mold. Most of the Cladosporium species do not grow at temperatures above 35°C.

Microscopic Features: Conidiophores are more or less distinct from vegetative hyphae. They may be erect, straight or flexuose, unbranched or branched only in the apical region, with geniculate sympodial elongation in some species. Conidia are produced in branched acropetal chains. Conidia are smooth, verrucose, or echinulate, one to four-celled, and they have a distinct dark hilum. Chains of conidia where the youngest conidium is at the apical or distal end of the chain are called blastocatenate.

Pathogenicity 

Cladosporium species are rare pathogens of humans but have been reported to cause infections of skin lesions, keratitis, onychomycosis, sinusitis, and pulmonary infections. The airborne spores of this genus are significant allergens. In large amounts, they can severely affect asthmatics and people with respiratory diseases too.

Laboratory Diagnosis 

Specimen: It depends on the nature of the infection site e.g. in the diagnosis of keratitis corneal scrapings (most frequent) or tissue biopsy and skin lesions (either cellulitis or metastatic lesions) and Nail clipping in onychomycosis. The clipping technique is simple and painless in which a fragment of at least 5 mm longitudinally and 2 mm transversely of the affected nail is cut with the help of a nipper.

KOH mount: Presence of fungal elements

Fungal culture: To obtain growth of fungi.

LPCB preparation: Observation of fungal structures from culture.

Serological test:  

The monoclonal antibody, EB-A2 used in the commercially available latex agglutination kit to detect galactomannan antigen in sera of patients with aspergillosis may cross-react with C. herbarum.

Histopathological Examination:  Brown (phaeoid) hyphae may be observed in infected tissue samples. When evaluating onychomycosis with PAS, the hypha is usually spotted in the ventral nail plate or subungual hyperkeratosis

Molecular Test:  PCR-based method, using sequencing identification as a gold standard but why this, it verifies as identification of Cladosporium species is often difficult due to the variability between isolates and because not all features required are always well developed. It is possible to identify the genus Cladosporium by several methods. On culturing, shield-shaped conidia, a distinct hilum, and chains of conidia are very common; however, to identify them at the species level is not easy. Therefore, molecular methods are needed. Some of the most commonly used molecular methods are the genus-specific confirmation by ITS and D1/D2 sequence analysis. Multilocus gene analysis of the ITS, D1/D2, EF-1α, and actin gene loci is necessary for accurate species identification.

Treatment

Very limited data are available on susceptibility profiles of Cladosporium spp. Useful anti-fungal drugs are-

• Itraconazole
• Voriconazole
• Amphotericin B and
• Posaconazole.

Keynotes

• Other genera similar to this genus are Toxicocladosporium, Penidiella, and Cladophialophora.
• Cladophialophora species ( C. bantiana, C. carrionii and C. devriesii) are thermotolerant with lacking conidiophores and unpigmented conidial scars.
• Cladosporium species grow easily on medium containing 10% glucose or 12–17% NaCl because of being osmotolerant.
• Odor in these organisms is due to volatile organic compounds (VOCs) and they do not produce any major mycotoxins.

References

1. https://en.wikipedia.org/wiki/Cladosporium
2. https://drfungus.org/knowledge-base/cladosporium
3. Medical Mycology. Editors:  Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
4. Rippon’s JW: Medical Microbiology. The pathogenic fungi and the Pathogenic Actinomycetes. 3^rd ed 1988 Publisher WB Saunder co, Philadelphia.
5. A Textbook of Medical Mycology. Editor: Jagdish Chander.  Publication Mehata, India.
6.  Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
7. https://www.healthline.com/health/cladosporium
8. https://mycology.adelaide.edu.au/descriptions/hyphomycetes/cladosporium/
9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390897/
10. https://www.sciencedirect.com/science/article/pii/S0166061618300095
11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087240/