Abstract
Infection with Aspergillus terreus is more likely to result in invasive, disseminated disease when compared to other Aspergillus species; importantly this species appears to be less susceptible to the antifungal drug amphotericin B. Unique to this species is the ability to produce specialized structures denoted as accessory conidia (AC) directly on hyphae both in vitro and in vivo. With the hypothesis that production of AC by A. terreus may enhance virulence of this organism, we analyzed the phenotype, structure and metabolic potential of these conidia. Comparison of A. terreus phialidic conidia (conidia that arise from conidiophores, PC) and AC architecture by electron microscopy revealed distinct morphological differences between the two conidial forms; AC have a smoother, thicker outer cell surface with no apparent pigment-like layer. Further, AC germinated rapidly, had enhanced adherence to microspheres, and were metabolically more active compared to PC. Additionally, AC contained less cell membrane ergosterol, which correlated with decreased susceptibility to AMB as determined using a flow cytometry based analysis. Furthermore, AC exhibited surface patches of β1-3 glucan, suggestive of attachment scarring. Collectively, the findings of this study suggest a possible role for AC in A. terreus pathogenesis.
Highlights
Aspergillus species remain the predominant etiological agents of invasive fungal infections among patients with hematologic malignancies and recipients of solid-organ and hematopoietic stem-cell transplants [1]
We demonstrate that A. terreus accessory conidia are phenotypically distinct, structurally, in cell wall composition, and in in vitro antifungal susceptibility, and as such may contribute to the virulence of this organism
All isolates were cultured on Sabouraud dextrose agar plates (SDA) and incubated at 37uC for three days after which phialidic conidia were harvested in phosphate-buffered saline (PBS), and 1,500 ml of the conidial suspension (56105 cells/ml) was transferred to 40 ml Sabouraud dextrose broth (SDB) with 0.1% Tween 20 (SDB Tween) [8]
Summary
Aspergillus species remain the predominant etiological agents of invasive fungal infections among patients with hematologic malignancies and recipients of solid-organ and hematopoietic stem-cell transplants [1]. The present study was designed with the following objectives: (1) to estimate AC production of a large number of A. terreus isolates recovered from both clinical and environmental samples, (2) to examine morphological differences between AC and PC, (3) to evaluate germination kinetics and metabolism of AC and PC, (4) to study differences in AMB susceptibilities of AC and PC using a flow cytometry based method, and (5) to analyze ergosterol content and b-glucan surface exposure of AC.
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