A 68-year-old man was admitted to the Burn Unit at University Medical Center with a 22% total-body-surface-area thirddegree burn. He underwent tangential excision and placement of split-thickness of allograft over his back and bilateral legs. A graft infection of the right knee produced a yellow-to-brown exudate that was submitted for culture.

Potassium Hydroxide (KOH) preparation of the exudate demonstrated large, distorted hyphae and budding yeast of varying sizes (Figure 1) which initially grew as moist, flat yeast on Sabouraud dextrose media. The yeast was identified as Mucor circinelloides by Matrix-Assisted Laser Desorption Ionization-TimeOf-Flight Mass Spectrometry (MALDI-TOF MS, bio-Merieux, Durham, North Carolina, USA).

A rapidly growing, off-white mold subsequently appeared on the primary mycology media. Microscopic examination of the mold by lactophenol cotton blue staining revealed unbranched sporangiophores supporting round sporangia (rhizoids were absent). These features were consistent with Mucor spp. (Figure 2).

M. circinelloides is the major human pathogen within the genus Mucor [1]. M. circinelloides may infect burned patients and has been responsible for lethal outbreaks in burn units [2]. Unlike other mucormycete molds, M. circinelloides is dimorphic, exhibiting mycelia in aerobic conditions and yeast in anaerobic/ high-CO₂ conditions [3]. The ability to transform into yeast under anaerobic conditions may explain the pathogenicity of this organism.

inding pleomorphic yeast and hyphae in burn wound exudate should lead to the clinical suspicion of M. circinelloides to allow rapid antifungal treatment of this dangerous mold.