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Penicillium on SDA

Penicillium on SDA, colonies are usually fast-growing, in shades of green, sometimes white, mostly consisting of a dense felt of conidiophores as shown above picture. They are cosmopolitan in distribution and are commonly called green mold. They are found in a variety of habitats like citrus fruits, jellies, foot stuff, old leather, paper, soil, etc. Conidia of Penicillium are present everywhere in air and soil and Penicillium was accidentally discovered by Alexander Fleming, who was working on bacteria and his culture got contaminated by Penicillium notatum. They are risk group one organism.

Classification

(Link (1809)

• Kingdom: Fungi
• Division: Ascomycota
• Class: Eurotiomycetes
• Order: Eurotiales
• Family: Trichocomaceae
• Genus: Penicillium

Some species of Penicillium are

1. Penicillium chrysogenum
2. Penicillium roqueforti
3. Penicillium notatum
4. Penicillium marneffei 

Structure and Reproduction of Penicillium

chains of single-celled conidia are produced in basipetal succession from a specialized conidiogenous cell called a phialide. 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). Mycelium is well developed and profusely branched. It is composed of colorless, slender, tubular, branched, and septate hyphae, and overall hyphae spread on the surface but some hyphae penetrate inside the substratum to absorb the nourishment. The mycelium becomes colored due to the production of colored conidia.  Hyphae is septate and each cell is uninucleate. The cell wall is microfibrillar, and in Penicillium notatum, it is of three ( 3) layers. The outer layer is made up of glucan while the next layer is made up of proteins and the final i.e. the 3rd layer is made up of chitin fibrils embedded in the granular matrix. The innermost layer is made up of pectic and hemicellulose. The plasma membrane surrounds the cytoplasm that contains organelles like mitochondria, ribosomes, and endoplasmic reticulum in the embedded form. The reserve food is in form of oil globules and the adjacent cells are connected by a pore present in the septa of their walls.

Penicillium reproduces by vegetative, asexual reproduction as well as sexual reproduction. Vegetative reproduction- It takes place by fragmentation. During fragmentation, the hyphae break into short fragments which grow by repeated division into new mycelium. Asexual reproduction-It takes place by the formation of conidia and conidia are produced on special hyphae called conidiophore and the conidia are erect, brown, and broom-like in fashion. Each branch bears a short branch at its tip, called metulae.  At each metula , there are bottle-shaped sterigmata.  Conidia are produced in chains at these sterigmata.  The whole group of metulae and sterigmata are called pencillus. Structure of conidia – Each conidium is a tiny, uninucleate, spore-like structure. It may be globose and ovoid in shape. The spore wall is pigmented and is made up of two layers. The outer layer is thick, pigmented is called exine whereas the inner layer is smooth, and thin is called intine.  Inside the spore wall, a plasma membrane is present, which encloses the mitochondria, ribosomes in the embedded form. The reserve food is in oil globules.

Medical Concern

Human pathogenic species are rare, however opportunistic infections leading to mycotic keratitis, otomycosis, and endocarditis. A major disease caused by Penicillium species is 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 third most common opportunistic infection in HIV – positive individuals. Human transmission does not occur.  Dissemination of infection occurs through the lymphatics or hematogenous.

Clinical features 

Various types of manifestations include:

• pyrexia ( fever) of unknown origin (PUO), loss of weight, generalized
  lymphadenopathy, anemia
• hepatomegaly with or without splenomegaly
• pneumonitis: cough and dyspnea occur in about 50% of cases,
  sometimes with hemoptysis

Laboratory manual for the diagnosis of fungal opportunistic infections in HIV/AIDS patients

• skin lesions – characteristic generalized papular eruptions, central
  umbilicated papules resembling those of molluscum contagiosum, or acne-like lesions and folliculitis over face, trunk,  and extremities
• pharyngeal and palatal lesions also can be seen subcutaneous nodules may be seen
• chest radiographic abnormalities typically manifest as diffuse reticulonodular infiltrates, and cavitations

 Laboratory Diagnosis of P. marneffei

1. Specimen: Bone marrow aspirate, blood, lymph node biopsy, skin biopsy,
   sputum, BAL, pleural fluid, liver biopsies, CSF, pharyngeal or palatal ulcer,
   scrapings, urine, stool, kidney biopsy, pericardium, stomach or intestinal
   specimens.
2. Giemsa, Wright, GMS, or PAS stain shows characteristic intracellular (within neutrophils or tissue histiocytes) round to oval yeast-like cells, which may divide by cross wall formation. The cross wall formation can differentiate yeast cells of P. marneffei from those of Histoplasma capsulatum. Elongated sausage-shaped extracellular forms are also seen.
3. Direct immunofluorescence test is the test of choice for specific diagnosis; this would be done at reference laboratories since it requires a fluorescent microscope.
4. Definitive diagnosis is based on culture isolation, which has high sensitivity – bone marrow (100%), blood (76%), and skin biopsies (90%). Penicillium marneffei exhibits thermal dimorphism by growing in living tissue or in the culture at 37°C as a yeast-like fungus, and in the culture at below 30°C as a mold.
5. Several serological methods for the detection of antibodies or antigens are attempted and produce conflicting results, especially in AIDS patients. e.g. commercially available Pastorex Aspergillus i.e. Latex Agglutination test kit
6. A specific PCR assay is under evaluation and might be useful as an alternative test for rapid diagnosis of Penicillium marneffei infection.

Treatment 

Useful anti-fungal drugs are-

• Amphotericin B
• Itraconazole
• Voriconazole
• Posaconazole

Key Notes

1. Penicillium is a very large and ubiquitous genus that currently contains 354 accepted species.
2. Many species of Penicillium are common contaminants on various substrates and are known as potential mycotoxin producers.
3. For identification, isolates are usually inoculated at three points on Czapek Dox agar and 2% Malt extract agar and incubated at 25°C.  Most species sporulate within 7 days Due to rapid growth.
4. The causative agent of Penicilliosis is  Penicillium marneffei.
5. Penicillium marneffei has transferred to the genus Talaromyces (Samson et al. 2011b).

#Related Videos#

Penicillium growth on SDA-

#Penicillium under the Microscope-

#Penicillium marneffei in LPCB preparation showing hyphae, conidiophores,conidia, and phialides as shown below-

#Penicillium cheresanum showing single-celled conidia as shown below-

Bibliography

1. Medical Mycology. Editors:  Emmons and Binford, 2nd ed 1970, Publisher Lea and Febiger, Philadelphia.
2. Rippon’s JW: Medical Microbiology. The pathogenic fungi and the Pathogenic Actinomycetes. 3^rd ed 1988 Publisher WB Saunder co, Philadelphia.
3. A Textbook of Medical Mycology. Editor: Jagdish Chander.  Publication Mehata, India.
4.  Practical Laboratory Mycology. Editors: Koneman E.W. and G.D. Roberts, 3rd ed 1985, Publisher Williams and Wilkins, Baltimore.
5. https://mycology.adelaide.edu.au/descriptions/hyphomycetes/talaromyces/
6. https://mycology.adelaide.edu.au/descriptions/hyphomycetes/penicillium
7. https://www.slideshare.net/SyedaFari2/penicillium
8. https://www.biologydiscussion.com/fungi/penicillium
9. https://en.wikipedia.org/wiki/Penicillium