Fungal Infections

Species name/ common name

Pneumocystis jirovecii (old name P. carinii)

Natural habitat

Human lung. People with Pneumocystis pneumonia cough and this disseminates the infection. Probably so well adapted to the human lung (co-evolution), that it has lost the ability to grow outside the lung. Other mammals have their own adapted species.


Worldwide. Possibly human and/or P. jirovecii genetic variation alters local prevalence. Antibody studies in children suggest extensive exposure early in childhood.


Common if sought carefully. Disease very rare unless immune system suppressed.


Pneumocystis pneumonia (PCP) may occur in AIDS or other immunocompromised patients. Uncertainty about its role in chronic obstructive airways disease exacerbations. P. jirovecii may disseminate rarely to the blood, eye, brain and skin.

Culture peculiarities

Unable to be cultured.

Antifungal resistance (intrinsic and acquired)

Resistant to all conventional antifungal drugs because ergosterol in cell wall is replaced with cholesterol. Illness responds to high doses of co-trimoxazole (trimethoprim/sulphamethoxazole), pentamidine, clindamycin and primaquine. May be prevented with dapsone, co-trimoxazole or atavaquone.

Biosafety level 2

As this organism is non-culturable, no specific rules regarding its lab handling exist.

Industrial use



Cluster of P. jirovecii stained with immunofluorescing
antibody, the best microscopic method for diagnosis


P. murina stained with rapid Wright-Giemsa. Clusters of P. murina from a homogenate of  infected mouse lung were dropped on glass slides and stained with a rapid Wright-Giemsa.  black arrow points to  cluster of trophic forms.  white arrow indicates a mature cyst. yellow arrow - an immature cyst. 10 um bar.


Cyst forms of P. jirovecii by scanning electron microscopy. Courtesy of Melanie Cushion, University of Cincinnati College of Medicine.





Microscopy of P. jirovecii stained with anti-glucan antibody (reacted with a mAB to β-1,3-D-glucan conjugated to Alexafluor 594). On the left the fungus can be seen under phase contrast microscopy. On the right under fluorescent microscopy, showing the antibody binding to glucan in the cell wall.  Courtesy of Melanie Cushion, University of Cincinnati College of Medicine  





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