Identification of mucorales from clinical specimens: a 4-year experience in a single institution

Mucormycosis, a fatal opportunistic infection in immunocompromised hosts, is caused by fungi belonging to the order Mucorales. Early diagnosis based on exact identification and multidisciplinary treatments is critical. However, identification of Mucorales fungi is difficult and often delayed, resulting in poor prognosis. This study aimed to compare the results of phenotypic and molecular identification of 12 Mucorales isolates collected from 4-yr-accumulated data. All isolates were identified on the basis of phenotypic characteristics such as growth rate, colony morphology, and reproductive structures. PCR and direct sequencing were performed to target internal transcribed spacer (ITS) and/or D1/D2 regions. Target DNA sequencing identified five Lichtheimia isolates, two Rhizopus microsporus isolates, two Rhizomucor pusillus isolates, one Cunninghamella bertholletiae isolate, one Mucor fragilis isolate, and one Syncephalastrum racemosum isolate. Five of the 12 (41.7%) isolates were incorrectly identified on the basis of phenotypic identification. DNA sequencing showed that of these five isolates, two were Lichtheimia isolates, one was Mucor isolate, one was Rhizomucor isolate, and one was Rhizopus microspores. All the isolates were identified at the species level by ITS and/or D1/D2 analyses. Phenotypic differentiation and identification of Mucorales is difficult because different Mucorales share similar morphology. Our results indicate that the molecular methods employed in this study are valuable for identifying Mucorales.