Name a common opportunistic pathogen in immunocompromised individuals.

Pneumocystis jirovecii is recognized as a common opportunistic pathogen that primarily affects immunocompromised individuals, particularly those with HIV/AIDS, but can also impact patients undergoing chemotherapy or those on immunosuppressive therapy. This organism is a fungus that resides in the lungs and can cause Pneumocystis pneumonia (PCP), which is characterized by severe respiratory distress.

In immunocompetent individuals, Pneumocystis jirovecii typically does not cause disease due to a well-functioning immune system. However, in those with weakened immunity, the body struggles to control the infection, which can lead to significant morbidity and mortality if not treated promptly.

This reflects the crucial role of opportunistic pathogens—microorganisms that exploit a compromised immune system to cause disease, contrasting with the other organisms listed, which are typically not classified as opportunistic in the same context or are less common in such scenarios.