Patient: Female, 48-year-old Final Diagnosis: Disseminated Prototheca zopfii • sepsis Symptoms: Diarhea • fatigue • fever • vomiting Medication: — Clinical Procedure: — Specialty: Infectious Diseases • Microbiology and Virology Objective: Rare disease Background: Prototheca spp. are common and found in various environments, including animal and human intestines, on the skin and in respiratory tissues, and colonizing fingernails. Few strains pathogenic for humans have been discovered. Here, we describe an infection by the pathogenic fungus species Prototheca zopfii in a patient. The infection was initially classified as a fungus based on colony morphology, fungal staining results, and growth in some fungi culture media (Sabouraud dextrose agar [SDA]). Reports of Prototheca spp. infections are increasing, often with poor outcomes. The use of matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) technique for identification has been widely described. Phenotypic identification depends on microscopic examination of the direct wet mount and after subculturing in blood and SDA using different stains that show a typical morphological characteristic of Prototheca spp . Case Report: A 48-year-old woman was diagnosed with a P. zopfii infection after 22 days of hospitalization in the critical care unit. The patient had profound febrile neutropenia and absolute neutrophil count (ANC) was zero, associated with hypotension and disseminated intravascular coagulation (DIC) 10 days after receiving the first cycle of chemotherapy for metastatic breast adenocarcinoma. Unfortunately, the patient died within 2 days of the initiation of treatment with amphotericin B. Conclusions: This case report highlights algae infections as a possible opportunistic infection type in patients with profound neutropenia, and we discuss the use of MALDI-TOF MS-based technology in detecting such infections and predicting poor prognosis, especially in patients with the disseminated form with underlying febrile neutropenia.