Abstract
New molecular identification techniques and the increased number of patients with various immune defects or underlying conditions lead to the emergence and/or the description of novel species of human and animal fungal opportunistic pathogens. Antifungal susceptibility provides important information for ecological, epidemiological and therapeutic issues. The aim of this study was to assess the potential risk of the various species based on their antifungal drug resistance, keeping in mind the methodological limitations. Antifungal susceptibility profiles to the five classes of antifungal drugs (polyens, azoles, echinocandins, allylamines and antimetabolites) were determined for 1698 yeast reference strains belonging to 992 species (634 Ascomycetes and 358 Basidiomycetes). Interestingly, geometric mean minimum inhibitory concentrations (MICs) of all antifungal drugs tested were significantly higher for Basidiomycetes compared to Ascomycetes (p<0.001). Twenty four strains belonging to 23 species of which 19 were Basidiomycetes seem to be intrinsically “resistant” to all drugs. Comparison of the antifungal susceptibility profiles of the 4240 clinical isolates and the 315 reference strains belonging to 53 shared species showed similar results. Even in the absence of demonstrated in vitro/in vivo correlation, knowing the in vitro susceptibility to systemic antifungal agents and the putative intrinsic resistance of yeast species present in the environment is important because they could become opportunistic pathogens.
Highlights
Among the estimated 1.5 million fungal species, approximately 200 species of yeasts and moulds associated with humans as commensals or pathogens are reported, according to the Colloquium of the American Academy of Microbiology on the fungal Kingdom (The Fungal Kingdom: Diverse and Essential Roles in Earth’s Ecosystem, June 2008, ASM http://academy. asm.org/)
Geometric mean minimal inhibitory concentrations (MICs) of all antifungal drugs tested were significantly higher for Basidiomycetes compared to Ascomycetes (p,0.001, Table 2)
Using the previously defined thresholds, the percentage of reference strains with resistance or decreased susceptibility to drugs was significantly higher for Basidiomycetes than for Ascomycetes (Table 3)
Summary
Among the estimated 1.5 million fungal species, approximately 200 species of yeasts and moulds associated with humans as commensals or pathogens are reported, according to the Colloquium of the American Academy of Microbiology on the fungal Kingdom (The Fungal Kingdom: Diverse and Essential Roles in Earth’s Ecosystem, June 2008, ASM http://academy. asm.org/). New yeast species are regularly recognized as opportunistic pathogens This can be explained by an increased awareness of invasive fungal infections and by improved techniques that allow better identification of fungal species based on polygenic analyses. There is an increasing number of patients with various immune defects (haematological malignancies, solid tumours, organ transplantation, immunosuppressive treatments, etc.) or underlying conditions (intensive care unit, indwelling catheter, prosthetic devices, broad spectrum antibiotics, etc.). This complex setting often prompts use of preemptive, prophylactic and prolonged curative antifungal treatments that can favour the emergence of resistant species or mutations in the drug target [6]. Derivatives of piperazines, pyridines and pyrimidines are used as fungicides for plant protection and have a mode of action similar to that of azoles [7]
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