Fungus or parasite or both: a diagnostic challenge.

Protothecosis is a rare opportunistic infection caused by achlorophilic algae Prototheca wickerhamii, mainly in immunocompromised hosts. Due to their morphologic appearance in routine culture media, they can often mimic yeast-like opportunistic pathogens such as Pneumocystis jirovecii. This can delay the identification of other culprit organisms. We present a fatal case of protothecosis in a 74-year-old immunosuppressed male with concomitant Pneumocystis jirovecii pneumonia (PJP). The presence of a coinfection along with resemblance in routine culture media and microbiological and histopathological staining can prove to be a diagnostic challenge and delay appropriate care of an immunosuppressed patient.