Phenotypic Switching and β‐N‐Acetylhexosaminidase Activity of the Pathogenic Yeast Trichosporon asahii

Abstract

The genus Trichosporon includes approximately 30 species, of which at least six are associated with infection (trichosporonosis): T. asahii, T. mucoides, T. asteroides, T. cutaneum, T. inkin, and T. ovoides (7, 9). The first two species are responsible for deep-seated infection, and the last four are involved in superficial infection, including white piedra. More than 90% of deep-seated trichosporonosis is caused by T. asahii. Most patients with deep-seated trichosporonosis have an underlying hematological malignancy or neoplastic disease, and neutropenia due to cytotoxic chemotherapy is the most common apparent risk factor for this infection. Deep-seated trichosporonosis due to T. asahii is life threatening with a high mortality rate and a very poor prognosis (10,16,29,31). In addition, T. asahii is relatively resistant to amphotericin B (21, 30), and the number of reports of deep-seated trichosporonosis in immunocompromised hosts caused by T. asahii has been increasing. Despite the increased frequency and poor prognosis, few of the virulence factors of this organism have been elucidated. Only human host defenses against this microorganism have been investigated (14,15). Several known virulence factors contribute to the pathogenicity of Candida albicans: the production of extracellular enzymes such as secreted aspartyl proteinase and phospholipase, phenotypic switching, and dimorphism (3,5,13,25

Current Knowledge of Trichosporon spp. and Trichosporonosis

“…Those authors observed that strains of the three major types usually developed two to five colony types and switched at a frequency of 10 2 to 10 4 when grown at 37°C, similar to that observed with Candida albicans and Cryptococcus neoformans (4,59,87). Most of the colonies switched irreversibly to the smooth type, which had the greatest beta-N-acetylhexosaminidase enzymatic activity compared with the parent type in all strains (84).…”

“…No other clinically relevant Trichosporon spp. have been shown to produce this enzyme (84). The same study also reported 4 different morphological types of colonies grown on Sabouraud dextrose agar (SDA), i.e., white farinose (69%), white pustular (18%), yellowish white (10%), and white cerebriform (3%).…”

Phenotypic Switching in Candida lusitaniae on Copper Sulfate Indicator Agar: Association with Amphotericin B Resistance and Filamentation

“…PS has been demonstrated and described for pathogenic yeasts, including C. albicans (3,12,15,16,19,20,21,23,25,26), Candida glabrata (2, 10, 22), T. asahii (9), and C. neoformans (7). As a manifestation of apparent developmental programming, PS confers phenotypic variability and environmental adaptation that facilitates the survival and/or pathogenic success of the organism.…”

“…Phenotypic switching is an attractive explanation for such phenotypic variations in C. lusitaniae, since switching has been documented for other pathogenic yeasts, including Candida albicans (3,12,15,16,19,20,21,23,25,26), Candida glabrata (2,10,22), Trichosporon asahii (9), and Cryptococcus neoformans (7). This mechanism permits an organism to adapt to environmental changes through selective gene expression, including changes in the fungal response to antifungal agents.…”

Invasive fungal infection caused by Trichosporon mucoides

“…В нескольких опубликованных случаях продемонстри-рована хорошая эффективность азолов против рода Trichosporon, однако есть сообщения и о мультиле-карственной устойчивости к амфотерицину B, флюци-тозину, флюконазолу, итраконазолу [14]. В недавних исследованиях новые триазолы -вориконазол, поза-коназол и равуконазол -показали хорошую эффек-тивность in vitro против Trichosporon [15]. С другой стороны, проведенные исследования свидетельству-ют о том, что эхинокандины -каспофунгин, анидула-фунгин -вряд ли будут эффективны против разно-видностей Trichosporon [16].…”