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Images in Mycology

Macroscopic and Microscopic Findings of Pseudallescheria boydii

YongWoo Choi,Nuri Na,Jong Soo Choi,Joonsoo Park
10.17966/JMI.2019.24.2.66 Epub 2019 July 03

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Abstract



Keywords



Conidiophore Pseudallescheria boydii Scedos- porium apiospermum



Pseudallescheria boydii (P. boydii) is a species of fungus classified in the Ascomycota1. Formerly known as Monosporium apiospermum, Scedosporium apiospermum is the anamorph of P. boydii1. Typically found in stagnant and polluted water, P. boydii has been implicated in the infection of immunocompromized and near-drowned pneumonia patients2. Diagnosis of P. boydii is possible through isolation of the fungus in culture or through cytology and histopathology in the tissues of diseased individuals3. The treatment of P. boydii infections is complicated by its resistance to many standard antifungal agents used to treat infections by filamentous fungi3.

On Saboraud Dextrose Agar, P. boydii colonies mature rapidly and are flat, white colored, and texture ranges from wooly to cottony1. The colonies become grayish or smoky-brown colored with age (Figure 1A); some laboratorians refer to a "house mouse gray" color3. The color of the colony is white initially but darkens to gray to black with maturity on the reverse side (Figure 1B). Microscopically, the conidia of P. boydii are unicellular, pale brown, and ovoid with truncated bases formed singly, in small clusters at the ends of the conidiophores, or from short annelid necks arising directly from the hyphae3. Conidiophores bearing annelids are of varying length and exhibit little differentiation from the vegetative hyphae1. Fascicles of conidiophores bound together in synemata are sometimes present and are a variation of the asexual state referred to as the Graphium synanamorph3. Large (50~ 250 μm) brown cleistiothecia of the sexual P. boydii may develop after 2~3 weeks of incubation and are likely to be found at the center of a colony3. Ascospores are yellow-brown and ellipsoidal in shape3.

Figure 1. (A) The colony on Sabouraud's dextrose agar after incubation at 25℃ for 2 weeks. The color of the colony is white in the center, but the color becomes darker as it grows outward. The texture of the colony ranges from wooly to cottony. (B) Image of colony shown in (A) taken from below. The colony had a black-gray colored crater-like structure. (C) The conidia of P. boydii were unicellular and ovoid with a truncated base (red arrow) at the ends of the conidiophores. Numerous septated hyphae are seen (green arrow). Lactophenol cotton blue preparation ×1,000. (D) In the mature state, numerous lemon-shaped ascospores are seen (lactophenol cotton blue preparation ×400).


References


1. Karen C, Michael A, Marie L, Alexander J, Robin P, Sandra S, et al. Manual of clinical microbiology. 12th ed. Wachington, DC: ASM Press, 2019:2007-2305

2. Guarro J, Kantarcioglu AS, Horré R, Rodriguez-Tudela JL, Cuenca E, Berenguer J, et al. Scedosporium apiospermun: changing clinical spectrum of a therapy-refractory opportunist. Med Mycol 2006;44:295-327
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3. Karoll J, Emmanuel R, Flavio Q, Joseph M, Charalampos A, Tena K, et al. Infections caused by Scedosporium spp. Clin Microbiol Rev 2008;21:157-197
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