Mycology notes on Penicillium

1. Name: Purshotam Kumar Sah Kanu
Roll No.: MB 1318/075
Level: M.Sc Microbiology (3rd Sem)
Central Department of Microbiology
Tribhuvan University, Kirtipur
Kathmandu, Nepal
MB 609 Systemic and Diagnostic
Mycology

2. Penicilliosis
 Penicillium species rarely cause opportunistic infections in
humans.
 The Penicillium species are identified by their typical
morphology (Fig. 74-6), culture characteristics on the SDA
medium (Color Photo 69), and microscopy (Color Photo
70).
 P. marneffei is the only dimorphic fungus in the genus
Penicillium known to cause opportunistic infection.
 There are more than 150 known species of the genus
Penicillium.

3. Cont..
 Fig. 75.9: Penicillium

4. Cont..
 P.marneffei causes disseminated infection in
immunocompromised hosts, such as patients with HIV.
 It develops a necrotizing reaction and involves the skin, lung,
and intestine.
 It causes disseminated infections of reticuloendothelial
system, and also allergic diseases and mycotoxicoses.
 The disseminated infection is more common in adults than in
children.
 P.marneffei is widely distributed in the nature.
 Its natural habitat is soil.

5. Cont..
 The fungus infects no mammals other than humans and
bamboo rat.
 Fungus is found in feces of rats and also in burrows made by
the rats in the soil.
 The infection is transmitted by inhalation of conidia, direct
inoculation of the skin, and rarely, by ingestion of infected
rats.
 The condition is more common in rainy season, in rural
areas.

6. Physiology
 The fungus, which is a dimorphic fungus, grows rapidly on
SDA.
 At 25°C, it grows as a mold and produces greenish yellow
 colonies with dark green edge and pink or red center.
 It exhibits brick red pigment on the reverse.
 At 37°C, it grows as small yeast, producing cream-colored
mucoid colonies resembling Histoplasma capsulatum.

7. Pathogenesis
 Incubation period is variable from few weeks to years.
 P.marneffei causes asymptomatic infections in immunocompetent
hosts.
 It causes granulomatous or suppurative reaction,
 Bronchopneumonia with or without adenopathy, and cavitary
lung lesion.
 It produces chronic cervical lymphadenitis resembling
tuberculosis.
 Disseminated infections occur rarely in immunocompetent hosts.

8.  P.marneffei causes disseminated infection in
immunocompromised hosts, such as patients with HIV.
 It develops a necrotizing reaction and involves the skin, lung,
and intestine.
 It causes disseminated infections of reticuloendothelial
system, and also allergic diseases and mycotoxicoses.
 The disseminated infection is more common in adults than in
children.

9. Epidemiology
 P.marneffei is widely distributed in the nature.
 Its natural habitat is soil.
 The fungus infects no mammals other than humans and
bamboo rat.
 Fungus is found in feces of rats and also in burrows made by
the rats in the soil.
 The infection is transmitted by inhalation of conidia, direct
inoculation of the skin, and rarely, by ingestion of infected
rats.
 The condition is more common in rainy season, in rural
areas.

10. Immunity
 Cell-mediated immunodeficiency, steroid treatment, and
HIV infection are predisposing factors.

11. Laboratory Diagnosis
1.Microscopy:
 Demonstration of P.marneffei in the skin and mucosal
scrapings, sputum, stool, blood, urine, lymph node, bone
marrow, lung and liver biopsy specimens.
2.Staining:
 Staining of skin, lymph node, and bone marrow aspirate by
hematoxylin and eosin, PAS (periodic acid-Schiff),Wright’s,
and calcofluor white stain demonstrates yeast cells with
transverse septa.

12. Cont..
3.Histological test:
 Immunohistochemical assay using monoclonal antibody
against an external wall epitope is used to identify P.marneffei
in tissues.
 Demonstration of fungal antigen in affected tissue by using
direct immunofluorescence antibody also helps in diagnosis
of the condition.
 Peripheral blood smear shows P.marneffei in patients with
AIDS.

13. Cont..
4.Culture:
 Culture is the gold standard. P.marneffei is a highly infectious fungus,
hence culture should be done in a laboratory with a biohazard safety
level-2 precautions.
 The fungus on SDA without cycloheximide and at 25°C produces
mycelial grayish white colonies, green center, white periphery, and
bright rose pigmented reverse (Color Photo 71).
 Microscopy of the colony shows septate hyaline hyphae, branched
conidiophores, and three to five medullae which produce phialides that
bear conidia in chains.
 The fungus on SDA at 37°C produces yeast-like colonies and cream-
colored mucoid with brown red pigment.
 Microscopy of the colony shows pleomorphic ellipsoidal to rectangular
yeast cells with transverse septum

14. COLOR PHOTO 71. SDA medium
showing colonies of Penicillium marneffei.
COLOR PHOTO 70. LPCB wet mount
showing Penicillium (×100).

15. Cont…
5.Serological test:
 Indirect immunofluorescent antibody test, immunoblot
assay, and immunodiffusion method using mycelial phase
culture antigen are used to demonstrate serum IgG
antibodies.
 Immunodiffusion and latex agglutination tests are used to
detect P.marneffei antigen in serum and urine.