Rapid and Robust Identification of the Agents of Black-Grain Mycetoma by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

Mark Fraser, Andrew M. Borman, Elizabeth M. Johnson

Eumycetoma, a chronic fungal infection endemic in India, Indonesia and parts of Africa and South and Central America, follows traumatic implantation of saprophytic fungi and frequently requires radical surgery or amputation in the absence of appropriate treatment. Fungal species that can cause black-grain mycetomas include Madurella spp., Falciformispora spp., Trematosphaeria grisea, Nigrograna mackinnonii, Pseudochaetosphaeronema larense, Medicopsis romeroi and Emarellia spp. Rhytidhysteron rufulum and Parathyridaria percutanea cause similar subcutaneous infections, but which lack the draining sinuses and fungal grains characteristic of eumycetoma. Accurate identification of the agents of subcutaneous fungal infection is essential to guide appropriate antifungal therapy. Since phenotypic identification of the causative fungi is often difficult, time-consuming molecular approaches are currently required. Here we have evaluated whether MALDI-ToF mass spectrometry might allow the accurate identification of eumycetoma agents and related fungi. A panel of 57 organisms corresponding to 10 different species from confirmed cases of eumycetoma and subcutaneous pedal masses, previously formally identified by PCR amplification and sequencing of ITS1, were employed. Representative isolates of each species were used to create reference MALDI-ToF spectra, which were then used for the identification of the remaining isolates in a user-blinded manner. Here, we demonstrate that MALDI-ToF mass spectrometry accurately identified all of the test isolates, with 100%, 90.4% and 67.3% of isolates achieving LogScores greater than 1.8, 1.9 and 2.0, respectively.