Cutaneous Infection Caused by Aspergillus ustus, an Emerging Opportunistic Fungus in Immunosuppressed Patients

Abstract

We report a case of primary cutaneous infection by the emerging fungus Aspergillus ustus in an immunosuppressed patient after a domestic accident. The patient failed to respond to itraconazole and died before receiving a new treatment with amphotericin B. There have been eight other cases reported since 1973, and only two patients survived the infection. In vitro susceptibility testing of seven antifungal drugs showed that terbinafine and the new azole derivative UR-9825 were the most active against this fungus.

Infections caused by Aspergillus species have increased dramatically in recent years, and, after Candida albicans, they are the most common cause of human opportunistic fungal infection in immunocompromised patients (7, 9). Aspergillus fumigatus is the species which most frequently causes invasive pulmonary aspergillosis, but more than 30 other species of the genus are associated with different human and animal infections (1). Aspergillus ustus is a species which is not frequently found in clinical specimens. However, in recent years it has been repeatedly reported as causing fatal infections in immunocompromised patients (8). Since 1973, eight cases have been described in the literature; the patients were mainly treated with amphotericin B, but the infection caused by A. ustus was solved in only two of them, in which this drug was combined with flucytosine or terbinafine. The infection sites have been almost exclusively the lung and the skin (8). Here, we report a case of primary cutaneous infection, probably as a result of a trauma, caused by A. ustus in an immunosuppressed patient.

A 77-year-old woman was admitted to the hospital in December 1998 after a domestic accident. She had fallen down the stairs at home, which caused contusions and an erosive cutaneous lesion on the dorsum of her left wrist. The lesion progressively worsened and became very painful. Past medical history revealed that she suffered from hypertension, which was treated with furosemide (20 mg/day) and potassium supplements. In September 1998, a nonsurgical right frontotemporal astrocytoma was diagnosed and she began palliative therapy with dexamethasone (4.5 mg/day). On examination, she presented an extensive (30- by 8-cm) ulcerative and erythematous plaque on the dorsum of her left forearm and hand, with granulomatous and suppurative borders (Fig. 1). She was treated with ciprofloxacin, amikacin, and clindamycin, together with topical gentamicin and an iodine solution, but the injury did not improve. The patient remained afebrile, and the rest of the physical examination was unremarkable, except for a significant loss in muscular strength. The abnormal laboratory findings included the following: hemoglobin, 10.8 g/dl; blood urea nitrogen, 15.5 mmol/liter; albumin, 32 g/liter; total proteins, 55 g/liter. Chest X ray was normal. Cultures of the exudate and of the biopsy material from the lesion on Sabouraud glucose agar (Difco Laboratories, Detroit, Mich.) yielded numerous and identical fungal colonies. Histological sections of biopsy material stained with hematoxylin and eosin, periodic acid-Schiff, and Giemsa revealed numerous irregularly shaped, hyaline, septate, and branched hyphae (Fig. 2A). The patient was subsequently treated with itraconazole (400 mg/day) and potassium permanganate soaks every 12 h. After 7 days, the lesion seemed to improve slightly, but subsequently it worsened again. Histological examination of new biopsy material and its cultures were positive for apparently the same fungus. All isolates were identical and were identified as Aspergillus sp. Amphotericin B treatment was ordered, but before it could be started she died from a progressive deterioration due to her underlying disease. Autopsy was denied.

FIG. 1.

Erythematous plaque on left forearm and hand, with granulomatous and suppurative borders.

FIG. 2.

(A) Giemsa stain of biopsy tissue from the left forearm showing segmented hyphae. (B and C) Conidiophore, conidia, and Hülle cells of A. ustus, FMR 6729. Bars, 10 (A and C) and 20 (B) μm.

Two isolates collected at different times were inoculated on malt extract agar (MEA; Difco), potato dextrose agar (PDA; Difco), and Czapek agar (Difco) and incubated at 25°C in the dark for identification purposes. Growth ranges of both isolates were similar in all media (30 to 35 mm in diameter after 7 days). Colonies on MEA were dense, cottony, brownish grey, and white at the periphery and had a yellow diffusing pigment. The colony features on PDA were similar, but a typical brownish exudate was produced. On Czapek agar the colonies were umbonate and at first felty and cream to pale yellowish, but they became pulverulent and olive-brown when the conidial structures matured, and an abundant yellowish exudate was produced. They were characterized microscopically by smooth, brown, thick-walled conidiophores up to 250 μm long by 5 μm wide, with biseriate conidial heads composed of metulae up to 6 μm long by 4 μm wide and phialides up to 6 μm long by 3.5 μm wide (Fig. 2B). The conidia were globose, 4 to 5 μm in diameter, and brown with very rough walls. Irregularly elongated, slightly curved, or twisted Hülle cells were profusely produced in all media (Fig. 2C). On the basis of the above-mentioned characteristics both isolates were identified as A. ustus. This species is the most cosmopolitan of the five species included in the section Usti (2). It is clearly different from the others because of its conidial ornamentation, the color and shape of the Hülle cells, and the conidiophore morphology (6). Living cultures of the strain are kept in the culture collection of the Faculty of Medicine in Reus, Spain, as FMR 6729 and have also been deposited in the Institute of Hygiene and Epidemiology, Brussels, Belgium (IHEM 16237), and in the Centraalbureau voor Schimmelcultures, Utrecht, The Netherlands (CBS 102278).

The in vitro activities of amphotericin B, flucytosine, ketoconazole, itraconazole, voriconazole, UR-9825, and terbinafine against the two isolates were determined by a broth microdilution method (5), mainly according to the guidelines of the National Committee for Clinical Laboratory Standards for molds (3). The test was carried out using RPMI 1640 medium buffered to pH 7 with 0.165 M morpholinepropanesulfonic acid (MOPS), an inoculum of 6 × 10⁵ CFU/ml, an incubation temperature of 30°C, an incubation time of 48 h, and an additive drug dilution procedure. MICs were 1 μg of amphotericin B per ml, >64 μg of flucytosine per ml, 8 μg of ketoconazole per ml, 4 μg of voriconazole per ml, 2 μg of itraconazole per ml, 0.5 μg of UR-9825 per ml, and 0.031 to 0.062 μg of terbinafine per ml. The results are similar to those reported recently by Verweij et al. (8), who tested 12 strains of A. ustus and demonstrated that terbinafine showed the highest in vitro efficacy. In our case, the new azole derivative UR-9825 (Uriach, Barcelona, Spain) was also very active. In all the previously published cases, the treatment consisted mainly of amphotericin B and/or itraconazole with unsuccessful results. This seems to correlate with our in vitro results and those of Verweij et al. (8), who obtained MICs of amphotericin B and itraconazole of 2 and 1 to 8 μg/ml, respectively. For filamentous fungi, MICs of these two drugs higher than 1 μg/ml had been interpreted as indicative of resistance (4). Terbinafine has been used very little as therapeutic treatment for A. ustus infections. However, in one of only two cases that were successfully treated, the patient received treatment with topical terbinafine. The patient underwent a liver transplant and showed a primary cutaneous infection, which was successfully treated with amphotericin B and terbinafine (7).

This case is evidence that A. ustus is increasingly a cause of severe infection in immunocompromised patients. Terbinafine seems to be the appropriate drug to treat it, and a future alternative could be the new antifungal UR-9825, although further studies are required to confirm this.