Identification and molecular characterization of Subramaniula asteroides causing human fungal keratitis: a case report

Abstract

Background: Keratitis due to by filamentous fungi are not easy to diagnose thus causing a delay in correct therapy. There are many descriptions of keratitis due to Candida, Fusarium and Aspergillus genera. Subramaniula genus has only recently been reported to cause human infections and there are few descriptions of eye infections due to this filamentous fungus. Diagnosis of fungal keratitis is usually based on microscopic and cultural techniques of samples obtained by corneal swabbing or scraping. Considering the amount of time required to obtain culture results it is wise to use other diagnostic methods, such as molecular analyses. Therapeutic options against these fungi are limited by low tissue penetration in the eye due to ocular barriers. We describe the first case of S. asteroides human keratitis treated with isavuconazole.

Case presentation: We describe a rare case of fungal keratitis unresponsive to antimicrobial treatment in a 65-year-old male patient without a history of diabetes or immunological diseases. He reported that the onset of symptoms occurred during a long holiday in Cape Verde Island. Initial treatment with topical antibiotics associated to steroids were ineffective, allowing a slow clinical progression of disease to corneal perforation. On admission in our Hospital, slit-lamp examination of the left eye showed conjunctival congestion and hyperemia, a large inferior corneal ulceration with brown pigment, corneal edema, about 3 mm of hypopyon and irido-lenticular synechiae. The slow clinical progression of the disease to corneal perforation and the aspect of the ulcer were consistent with a mycotic etiology. Molecular methods used on fungal colonies isolated by Sabouraud's dextrose agar cultures allowed the identification of Subramaniula asteroids from corneal scraping. Antimicrobial test showed a good susceptibility of this filamentous fungus to voriconazole and isavuconazole. Moreover, this fungal keratitis was successfully treated with isavuconazole, without side effects, observing a progressive clinical improvement.

Conclusions: Molecular methods may be useful for the identification of filamentous fungal keratitis on scraping samples thus shortening the time of diagnosis. Systemic therapy by isavuconazole could be useful to treat the filamentous fungal keratitis, reducing the possible adverse effects due to the use of voriconazole by systemic administration.

Keywords: Case report; Fungal keratitis; Isavuconazole; Molecular identification; Subramaniula asteroides; β-Tubulin gene.

Fig. 1

a Slit lamp picture taken on initial presentation in our Hospital showing an inferior corneal ulceration with brown pigment (red arrow) and about 3 mm of hypopyon (yellow arrow) in the left eye. b Anterior segment optical coherence tomography (AS-OCT) showing the depth of the ulcer (white arrow)

Fig. 2

Macroscopic view colonies after one week of incubation on: a Chocolate Agar plate (CHOC); b BCG agar plate; c Sabouraud Dextrose Agar plate; d-g Microscopic view 0,25% Lugol stain. Microscopic description: hyphae broad, septate, hyaline, turning dark brown with age. Conidiophores phialidic, terminal or intercalary, short, hyaline, obclavate or cylindrical. Conidia hyaline, unicellular, obovoidal or ellipsoidal

Fig. 3

Two months after treatment non signs of active infection. A residual para-central corneal scar (white arrow) limits the visual acuity to 20/50