Fatal Pulmonary Mucormycosis Caused by Rhizopus microsporus in a Patient with Diabetes

Mucormycosis is an opportunistic infection caused by fungi of the order Mucorales, environmental nonseptate molds widely distributed in soil, plants, and decaying materials [1]. Mucormycosis can be divided into the following categories on the basis of the site of infection: rhinocerebral, pulmonary, cutaneous, and disseminated [2-4]. The most common clinical presentation is rhinocerebral disease, followed by pulmonary infection. Medically important Mucorales are Lichtheimia, Absidia, Mucor, Rhizomucor, Rhizopus, Cunninghamella, and Syncephalastrum. Identification of Mucorales is primarily based on standard mycological methods. However, culture-based identification is often difficult and time-consuming. Conventional phenotypic methods usually identify isolates only to the genus level, and sometimes only as Mucorales. In recent years, internal transcribed spacer (ITS) sequencing has been applied to fungi and is considered a reliable method for the accurate identification of most pathogenic Mucorales to the species level [5]. However, a few species have high ITS sequence homology, making their differentiation difficult. Here we report a case of fatal pulmonary mucormycosis caused by Rhizopus microsporus in an 83-yr-old man newly diagnosed with diabetes. The isolate was identified by a combination of phenotypic methods and genetic sequencing of the ITS and D1/D2 domains. An 83-yr-old man was referred to a tertiary hospital because of the increased sputum with dyspnea. He had a history of pulmonary tuberculosis in his 20s. Fasting blood glucose was 210 mg/dL, and hemoglobin A1c was 8.4% on initial laboratory tests. He was newly diagnosed with diabetes mellitus. His chest computed tomography (CT) scan revealed large cavitary lesions in the upper lungs (Fig. 1). Acid-fast staining and bronchoalveolar lavage fluid culture yielded negative results. On the fifth day of hospitalization, the serum Aspergillus galactomannan index value was slightly increased at 0.87 (threshold, 0.5). With a diagnosis of suspected pulmonary aspergillosis, itraconazole therapy (400 mg bid) was initiated. Fungus culture of bronchoalveolar lavage fluid was performed on Sabouraud dextrose agar at room temperature. After 3 days of incubation, white, aerial, cotton candy-like colonies appeared and quickly covered the agar surface (Fig. 2). These colonies turned pale brownish gray and light yellow reverse with time. Sputum culture on Sabouraud dextrose agar revealed the same colonies. Microscopic examination showed broad, unseptated hyphae. Sporangiophores were unbranched and arose singly or in groups from above rhizoids. Sporangia were spherical, brown, and filled with sporangiospores (Fig. 3). The organism was provisionally identified as a Rhizopus species on the basis of colony morphology and microscopic features. Antifungal therapy was switched to intrave-