Pleurostomophora ochracea, a novel agent of human eumycetoma with yellow grains

Abstract

The first yellow-grain fungal mycetoma, in a 60-year-old man from Central Sudan, is reported. Morphological and phylogenetic analysis of the ribosomal small subunit (SSU), large subunit (LSU), internal transcribed spacer (ITS), β-tubulin (BT2), actin (ACT1), and elongation factor (TEF1) genes revealed that the isolate deviated from any known agent of mycetoma; it clustered in the genus Pleurostoma (anamorph genus, Pleurostomophora) in the order Calosphaeriales. The novel species, here named Pleurostomophora ochracea, is characterized by phenotypic features. The species proved to be highly susceptible to itraconazole, ketoconazole, posaconazole, and voriconazole, but not to fluconazole. The fungus was inhibited by caspofungin at 8 μg/ml, while no inhibition was found with 5-flucytosine (MIC > 64 μg/ml). Compared to other members of the genus Pleurostomophora, P. ochracea is slow growing, with a relatively high optimum growth temperature (36 to 37°C). This is the first case of a yellow-grain fungal mycetoma; yellow grains are otherwise of bacterial nature. Our case emphasizes that identification of mycetoma agents by the color of the grain only is not sufficient and may lead to inappropriate therapy.

Fig 1

Clinical presentation of the patient. (A) The patient had a mycetoma on the right foot, with massive, recurrent foot swelling. (B) On the foot X-ray, a massive soft tissue swelling, a periosteal reaction, and bone destruction are seen.

Fig 2

Phylogram of two loci (SSU and LSU) obtained by Bayesian analysis, maximum likelihood, and maximum parsimony (values of >0.8 for Bayesian probability and >80% for maximum likelihood and maximum parsimony are shown with thick branches). Leotia lubrica and Crinula caliciiformis were used as the outgroup. The portion of the phylogram relating to Calosphaeriales is shaded. The names of families within the order and the new isolate are shown in bold.

Fig 3

Phylogenetic tree resulting from Bayesian analysis, maximum likelihood, and maximum parsimony for the ITS gene (values of >0.8 for Bayesian probability and >80% for maximum likelihood and maximum parsimony are shown with thick branches). Togninia minima, Phaeoacremonium inflatipes, and Phaeoacremonium aleophilum were used as the outgroup. Light-gray circles, strains isolated from plants; dark-gray circles, human-pathogenic strains.

Fig 4

Colony diameters after 1 month of incubation at various temperatures ranging from 15 to 36°C at 3°C intervals, including 10°C, 37°C, and 40°C.

Fig. 5.

P. ochracea growth and morphology. Shown are colonies after 2 weeks of incubation at 37°C. (A) PDA. (B) MEA. (C) OA. (D, E, and F) Different-shape conidia. (G, H, and I) Type I phialides. (J, K, and L) Type II phialides. (M, N, and O) Type III phialides. All scale bars, 10 μm.