Light micrograph of Pneumocystis jirovecii fungal cysts (purple ovals) in a lung tissue impression smear sample. Pneumocystis fungi have both asexual and sexual life stages. The cysts contain the spores (reproductive cells) of the sexual stage. P. jirovecii spreads from person to person through the air and can cause pneumocystis pneumonia (PCP). Patients on medications such as corticosteroids and immunocompromised patients are at the greatest risk of infection. Symptoms of PCP include fever, coughing and difficulty breathing. If left untreated PCP can lead to death. Treatment is most often with antibiotics such as trimethoprim or sulfamethoxazole. Sample stained by the toluidine blue method.