[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Yeasts and yeast-like fungi](https://durgical.com/en/microbiology/groups/yeasts-and-yeast-like-fungi/) › Pneumocystis jirovecii [Microbiology](https://durgical.com/en/microbiology/) · [Yeasts and yeast-like fungi](https://durgical.com/en/microbiology/groups/yeasts-and-yeast-like-fungi/) # Pneumocystis jirovecii - Fungus - Exam priority: medium An atypical fungus that cannot be cultured; it causes severe pneumonia in advanced HIV or other immunosuppression. Prevented with trimethoprim-sulfamethoxazole. Updated 2026-11-01 Also called: Pneumocystis, formerly P. carinii ## Key points - A fungus that stains with silver and cannot be cultured - HIV with CD4 below 200: trimethoprim-sulfamethoxazole prophylaxis - Bilateral ground glass, high LDH and hypoxemia - Corticosteroids if hypoxemia is significant - Azoles and amphotericin B are useless (no ergosterol) ## At a glance **Shape** Round or cup-shaped cysts, sometimes crushed **Family** Pneumocystidaceae (Taphrinomycotina) **Type** Atypical fungus (once thought a protozoan); cysts and trophic forms; not culturable **Stain** Silver (GMS): cyst wall; Giemsa: trophic forms; direct immunofluorescence **Size** Cysts of about 4–7 µm ## Morphology - Thick-walled cysts that stain with silver and often look wrinkled or cup-shaped - Small trophic forms that stain with Giemsa - Its membrane has cholesterol instead of ergosterol - Does not grow in culture media ## Transmission - Airborne, from person to person - Healthy adults can carry it without symptoms and pass it on - Most children are infected in early years without falling ill **Reservoir:** Humans (asymptomatic carriers) ### Isolation precautions What the care team adds to standard precautions. - Standard ## Virulence factors - Attaches to type I pneumocytes and fills alveoli with a foamy exudate - Without ergosterol it escapes azoles and amphotericin B - Variable surface glycoproteins that evade the immune response ## Diseases it causes - Pneumocystis pneumonia: dry cough, fever and progressive breathlessness with hypoxemia [Pneumocystis pneumonia (PCP) →](https://durgical.com/en/conditions/pneumocystis-pneumonia/) - An AIDS-defining illness, typical with CD4 below 200 cells/µL [HIV infection and AIDS →](https://durgical.com/en/conditions/hiv-infection-and-aids/) ## Clinical picture - Desaturation on exertion with a nearly normal lung exam - Bilateral ground-glass opacities on X-ray or CT - Risk of pneumothorax - In people without HIV (transplant, steroids) the course is faster and more severe ## Diagnosis - Bronchoalveolar lavage or induced sputum with silver (GMS) or direct immunofluorescence - PCR on a respiratory sample - Raised serum beta-D-glucan (supportive) - Raised LDH and bilateral ground glass on CT ## Treatment Trimethoprim-sulfamethoxazole (folate synthesis inhibitors) is the treatment of choice; alternatives are pentamidine, atovaquone, and primaquine with clindamycin. Corticosteroids are added for moderate or severe hypoxemia. Classic antifungals do not work. Drug class only; doses and regimens are set by the clinician from the current guideline. In Pharmacology: - [Dapsone](https://durgical.com/en/pharmacology/dapsone/) - [Pentamidine](https://durgical.com/en/pharmacology/pentamidine/) ## Prevention - Trimethoprim-sulfamethoxazole prophylaxis in HIV with CD4 below 200 cells/µL, in transplant recipients and with prolonged corticosteroids - Prophylaxis alternatives: dapsone, atovaquone or inhaled pentamidine - Antiretroviral therapy to restore CD4 - Avoid sharing a room with other immunosuppressed patients ## Memory aid Silver cysts below 200: the cysts shine with silver stain, and prophylaxis starts once CD4 falls under 200. ## Test yourself Think of the answer, then tap the question to see it. ## At what CD4 count is Pneumocystis prophylaxis started in people with HIV? When CD4 is below 200 cells/µL (also with oropharyngeal candidiasis). ## Which drug class is used to treat and prevent Pneumocystis pneumonia? Trimethoprim-sulfamethoxazole, a combination that blocks folate synthesis. ## Why does Pneumocystis not respond to amphotericin B or azoles? Its membrane has cholesterol instead of ergosterol, the target of those antifungals. ## Which stain shows Pneumocystis cysts in bronchoalveolar lavage? Gomori methenamine silver (GMS); direct immunofluorescence is also used. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/pneumocystis-jirovecii/) ## Related - [Cryptococcus neoformans](https://durgical.com/en/microbiology/cryptococcus-neoformans/) - [Histoplasma capsulatum](https://durgical.com/en/microbiology/histoplasma-capsulatum/) ## Related conditions - [Pneumocystis pneumonia (PCP)](https://durgical.com/en/conditions/pneumocystis-pneumonia/) - [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. [← Back to the group: Yeasts and yeast-like fungi](https://durgical.com/en/microbiology/groups/yeasts-and-yeast-like-fungi/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Pneumocystis Pneumonia Basics](https://www.cdc.gov/pneumocystis-pneumonia/about/index.html) (CDC, 2024); [Pneumocystis jirovecii pneumonia: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000671.htm) (MedlinePlus (NLM), 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/pneumocystis-jirovecii/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/pneumocystis-jirovecii/