In Vitro Activities of Antifungal Combinations against Biofilms and Planktonic Forms of Clinical Trichosporon asahii Isolates

Abstract

T richosporon species can cause biofilm-associated infections related to indwelling medical devices, especially intravenous catheters, and unacceptable mortality rates have been reported despite the administration of antifungal treatments (1). Trichosporon asahii can form biofilms with structured microbial communities in vitro, embedded within an extracellular matrix, with significantly increased resistance to antifungal compounds (2, 3), which might ultimately lead to clinical treatment failure. Antifungal combination may be an alternative therapy strategy for biofilm-related fungal infections (4). The synergistic effects of antifungal combinations against other fungal biofilms have been detected in vitro, such as amphotericin B-posaconazole for Candida albicans (5) and amphotericin B-caspofungin or voriconazole-caspofungin for Aspergillus spp. (6). The synergistic effects of antifungal combinations of voriconazole, amphotericin B, and caspofungin against planktonic T. asahii have been found in vitro (7). We evaluated the in vitro activity of the combinations of voriconazole-amphotericin B, voriconazole-caspofungin, and amphotericin B-caspofungin against 16 clinical isolates of T. asahii in biofilm and planktonic forms by a broth microdilution checkerboard method (5). Trichosporon biofilms were prepared according to the 96-well plate-based method (8). The effect of antifungal agents was determined by the 2,3-bis(2-methoxy-4-nitro-5-[(sulfenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT)-based colorimetric assay for both biofilms and planktonic cells (5,8). The MIC and sessile MIC (SMIC) were determined as the lowest antifungal concentration (alone or in combination) that caused a 50% reduction in optical density for both biofilms and planktonic cells compared with the growth control (5, 6). The interaction was defined on the basis of the fractional inhibitory concentration indexes (FICIs) as follows: Յ0.5, synergy; Ͼ0.5 to 4, indifference; and Ͼ4.0, antagonism.Under planktonic conditions, the amphotericin B-caspofungin combination showed the highest percentage of synergistic effects (81.25%; FICI, 0.125 to 0.5) ( Table 1), as indicated by a previous in vitro study (7). Under biofilm conditions, the voriconazole-amphotericin B combination showed the highest percentage of synergistic effects (87.5%; FICI, 0.078 to 0.313), and the SMIC 90 /SMIC ranges for these two drugs obviously decreased from Ͼ1,024/512 to Ͼ1,024 g/ml to 64/4 to 128 g/ml for voriconazole and from 1,024/32 to 1,024 g/ml to 32/4 to 128 g/ml for amphotericin B, respectively. The combinations of amphotericin B-caspofungin (93.75%) and voriconazole-caspofungin (81.25%) mainly yielded indifferent interactions, and no antagonistic interaction was observed in any of the combinations of either the biofilms or the planktonic forms of T. asahii isolates (Table 1).Trichosporon now ranks as the second most common pathogen causing fungemia in patients with hematological malignant disease, mainly catheter-related bloodstream infections (CR-BSIs) (1, 9). For ...

Trichosporon inkin biofilms produce extracellular proteases and exhibit resistance to antifungals

“…On the other hand, T. inkin biofilms were tolerant to higher concentrations of all antifungals tested. Similar results were found by Di Bonaventura et al (2006), Iturrieta-González et al (2014) and Liao et al (2014), who reported that, although Trichosporon spp. planktonic cells were susceptible to voriconazole and fluconazole, their biofilm counterparts were resistant to azoles, amphotericin B and caspofungin.…”

“…Biofilms produced by Trichosporon spp. also presented higher tolerance to antifungals (Di Bonaventura et al, 2006;Iturrieta-González et al, 2014;Liao et al, 2014;Sun et al, 2012). Data from the present study reveal that planktonic cells showed susceptibility to azoles and resistance to amphotericin B and caspofungin.…”

“…Experiments were conducted in duplicate and controls were grown in RPMI without antifungals. Minimum biofilm inhibitory concentration (MBIC) was defined as the lowest concentration able to inhibit 100 % of biofilm growth for AMB (Di Bonaventura et al, 2006) and 50 % for the remaining antifungals (Liao et al, 2014), when compared to drug-free controls. Susceptibility testing of planktonic cells was performed in accordance with CLSI (2008).…”

“…Despite the importance of this subject, there are few reports on Trichosporon spp. biofilms (Di Bonaventura et al, 2006;Dostálková et al, 2015;Iturrieta-González et al, 2014;Junqueira et al, 2012, Lakshmi & Das, 2013Liao et al, 2014Liao et al, , 2015Sun et al, 2012).…”

Biofilm Production and Antibiofilm Activity of Echinocandins and Liposomal Amphotericin B in Echinocandin-Resistant Yeast Species

“…Liposomal amphotericin B had the highest activity against biofilms formed by isolates with acquired resistance (the P value was not significant) or intrinsic resistance (P Ͻ 0.05) to echinocandins; this finding is consistent with other studies, where conventional amphotericin B had high anti-biofilm activity, even against non-Candida isolates (25)(26)(27)(28)(29). However, we observed that biofilms formed by C. tropicalis isolates were highly resistant to liposomal amphotericin B, which was unable to achieve an 80% reduction in the metabolic activity of the biofilm.…”