Acrophialophora fusispora Misidentified as Scedosporium prolificans

Comment Letter 1

Arthur et al. reported an interesting case of human keratouveitis associated with the long-term intraocular retention of a contact lens, in which a filamentous fungus and Staphylococcus aureus were involved (1). In spite of no antifungal drug being administered, the infection was resolved. Histological examination revealed the presence of fungal elements in the tissue around the lens.

The fungus involved in such infection was identified by the authors as Scedosporium prolificans (1), an emerging hyphomycete which causes severe infections, mainly in immunocompromised patients (3). However, it was described as having “flask-shaped conidiogenous cells with elongated necks and individual conidia as well as chains…” (1). Scedosporium prolificans is indeed characterized by flask-shaped conidiogenous cells, often in brush-like arrangement, not single on hyphae as depicted in Fig. 2 of the mentioned article, and by its ovoid conidia in slimy heads, never in chains. This last feature is useful to inexperienced mycologists for distinguishing this species from other morphologically similar fungi such as Scopulariopsis spp. Some species of Scopulariopsis show dark colonies and also dark conidia, which arise from annellidic conidiogenous cells, forming dry, basipetal chains. However, the fungus shown in Fig. 2 does not seem to be a species of Scopulariopsis, because in this genus single conidiogenous cells are not common. They are mainly in branched and sometimes penicillated conidiophores. Furthermore, conidia of Scopulariopsis spp. are more or less spherical and usually with a wide truncate base, while those of Fig. 2 seem to be fusiform or lemon-shaped.

It is difficult, merely by observing the mentioned figure, to ascertain the species to which the fungus belongs. However, the images are reminiscent of Acrophialophora fusispora, which has been recovered recently in several clinical cases. Its colonies are greyish brown, and the conidia are pale brown. An important distinctive feature of this species is the ornamentation of the conidia, which is finely echinulate and often with distinct spiral bands. Acremonium sp. could be another possibility due to the presence of single conidiogenous cells (phialides) emerging from ropes of vegetative hyphae (Fig. 2B), which is typical of this genus, although dark colonies are rarely produced.

To provide figures of a fungus involved in a reported case, even if the species is common, constitutes a good practice. This allows readers to agree or not, as in this case, with the identification of species involved. We would like to encourage the authors to deposit cultures of clinical isolates in an international culture collection, from where it could then be obtained by interested people for further studies. Without the availability of the isolates, the published etiology is of low value (2).