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Penicillium Growth on SDA

Penicillium growth on SDA as shown above picture. Penicillium is a genus of ascomycetous fungi that is of major importance in the natural environment as well as in food spoilage, and even in food and drug production. Some members of the genus ( P. notatum)  produce penicillin, a molecule that is used as an antibiotic, which kills or inhibits the growth of certain kinds of bacteria. Other species are used in cheese making such as Roquefort (Penicillium roqueforti-blue cheese) and camembert (Penicillium camemberti). According to the Dictionary of the Fungi (10th edition, 2008), the widespread genus contains over 300 species but recent data shows 354 accepted species (Visagie et al. 2014). They are common contaminants on various substrates and are known as potential mycotoxin producers. Correct identification is thus important when studying possible Penicillium contamination of food. Medically important species are rare, however opportunistic infections leading to mycotic keratitis, otomycosis and endocarditis have been reported (Lyratzopoulos et al. 2002).

Classification of Penicillium

Link (1809)

• Kingdom: Fung
• Division: Ascomycota
• Class: Eurotiomycetes
• Order: Eurotiales
• Family: Trichocomaceae
• Genus: Penicillium
• Species:  Penicillium chrysogenum,

Penicillium citrinum,

Penicillium janthinellum,

Penicillium marneffei,

 Penicillium purpurogenum

Morphology of Penicillium

Macroscopic features-

Other than P. marneffei colonies are usually rapid growing, in shades of green, sometimes white, mostly consisting of a dense felt of conidiophores. Whereas P.  marneffei is thermally dimorphic and produces filamentous, flat, radially sulcate colonies at 25°C. These colonies may be bluish-gray-green at the center and white at the periphery. The red, rapidly diffusing, soluble pigment observed from the reverse is very typical.  Colonies become cream to slightly pink in color and glabrous to convoluted in texture at 37°C.

Microscopic Features-

1. Microscopic structures consist of conidia, conidiophores, phialides, metulae. Conidia are chains of single-celled are produced in basipetal succession from a specialized conidiogenous cell called a phialide.
2. The term basocatenate is often used to describe such chains of conidia where the youngest conidium is at the basal or proximal end of the chain. In Penicillium, phialides may be produced singly, in groups, or from branched metulae, giving a brush-like appearance (a penicillus).
3. The penicillus may contain both branches and metulae (penultimate branches which bear a whorl of phialides).
4. All cells between the metulae and the stipes of the conidiophores are referred to as branches.
5. The branching pattern may be either simple (non-branched or monoverticillate), one-stage branched, two-stage branched, or three- to more-staged branched. Conidiophores are hyaline, smooth, or rough-walled.
6. Phialides are usually flask-shaped, consisting of a cylindrical basal part and a distinct neck, or lanceolate. Conidia are in long dry chains, divergent or in columns, are globose, ellipsoidal, cylindrical or fusiform, hyaline or greenish, smooth or rough-walled.
7. Sclerotia are produced by some species and they are the hard dark resting body consisting of a mass of hyphal threads, capable of remaining dormant for long periods.

Pathogenicity

Major diseases are caused by Penicillium species Talaromycosis (formerly Penicilliosis). Penicilliosis is an infection caused by Penicillium marneffei, a dimorphic fungus endemic to Southeast Asia and the southern part of China. It is the 3rd most common opportunistic infection in HIV-positive individuals. Human to human transmission does not occur. Dissemination of infection occurs through the lymphatics or hematogenous. Other than P. marneffei may also cause opportunistic infections leading to mycotic keratitis, otomycosis, and endocarditis.

Symptoms of Penicilliosis

Common symptoms include fever, sweats, skin lesions, and often papules with central umbilication or nodules, but a wide range of skin eruptions are possible.

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) while in otitis media ear discharge. Other samples may also bone marrow examination and less reliably from blood cultures be used.

KOH mount: Presence of fungal elements

Fungal culture: To obtain the 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 penicilliosis. Galactomannan (GM) is a heteropolysaccharide in the cell walls of most Aspergillus and Penicillium species.

Cytological and Histological Examination 
The diagnosis of penicilliosis may be suspected or made through examination of cytology or biopsy specimens. Cytology specimens are more readily obtained by less invasive procedures such as FNAC of lymph nodes, sputum cytology, and touch smear of skin. For high-grade fungemia, yeast cells may be seen inside monocytes in peripheral blood smears.  The yeast cells may be sparse or abundantly found in histiocytes or extracellularly and are most readily demonstrated by fungal stains such as periodic acid-Schiff (PAS) and silver methenamine stains. Detection of non-budding yeast cells with characteristic central transverse septum would give a presumptive diagnosis which should be confirmed by microbiological culture.

Molecular test: ITS and/or β-tubulin loci are recommended for the identification of Penicillium species.

Treatment

Treatment consists of amphotericin B followed by itraconazole. Other supportive antifungal drugs like ketoconazole and voriconazole may also be used.

Keynotes

1. Penicillium marneffei and other subgenus Biverticillium species have been transferred to the genus Talaromyces (Samson et al. 2011b).
2. The mortality rate of untreated penicilliosis is 100% in HIV-positive.
3. Penicillium is similar to genus Paecilomyces, Gliocladium, and Scopulariopsis. Penicillium differs from Paecilomyces by having flask-shaped phialides. It also differs from Gliocladium due to globose to subglobose conidia; by having chains of conidia; and from Scopulariopsis by forming phialides. P. marneffei differs as well by its thermally dimorphic nature.
4. Hyphomycete, flask-shaped phialides arranged in groups from branched metulae forming a penicillus are key features of this Penicillium.
5. Penicillium verrucosum produces ochratoxins.
6. Penicilliosis can clinically resemble tuberculosis, molluscum contagiosum, cryptococcosis, and histoplasmosis. The successful treatment of P. marneffei infection is dependent on its rapid and accurate diagnosis.

References

1. https://www.slideshare.net/Gowthamfarms/penicillium
2. https://mycology.adelaide.edu.au/descriptions/hyphomycetes/penicillium/
3. https://en.wikipedia.org/wiki/Penicillium
4. https://drfungus.org/knowledge-base-penicillium
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3038620/
6. https://www.tandfonline.com/doi/abs/10.1080/02681219480000701?journalCode=immy19
7. https://worldwidescience.org/topicpages/h/human+pathogen+penicillium.html