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doi:10.3389/fmicb.2016.00617. colonization in the airway tracts and existence in such proximity to humans generate risks for biofilm formation, which is a prerequisite event toward the development of invasive disease and has been reported to be involved in about 80% of nonacute infections in humans (6). Unlike the planktonic form, fungal biofilms are relatively resistant to conventional antifungal agents (6). biofilms have been demonstrated to exhibit a higher resistance to the tested compounds than the organism’s planktonic cells (7) and biofilms of (8). It has been demonstrated that tacrolimus (also known as FK506), which targets calcineurin, a Ca2+-calmodulin-dependent protein phosphatase that is important in various process in fungi, synergizes with azoles against planktonic cells and biofilms of spp. and (9, 10). Rabbit polyclonal to HPSE2 Thus, it is reasonable to suspect that the combination of FK506 and azoles would also generate synergy against planktonic cells and biofilms of and one control strain of (ATCC 22019) were studied. All strains were all clinical isolates and identified by microscopic morphology and by molecular sequencing of the internal transcribed spacer (ITS) ribosomal DNA (rDNA), as required. All tested agents, including FK506, itraconazole (ITC), posaconazole (POS), and voriconazole (VRC), were purchased in powder form from Sigma Chemical Co., St. Louis, MO, and prepared as outlined in CLSI document M38-A2 (11). The interactions between FK506 and azoles against planktonic cells and biofilms of were tested via the microdilution checkerboard technique, adapted from the CLSI broth microdilution method M38-A2 (11). The working concentration ranges of azoles and FK506 were 0.015 to 8 g/ml and 0.25 to 16 g/ml against planktonic cells and 0.5 to 64 g/ml and 1 to 64 g/ml against biofilm cells, respectively. The MICs applied for the evaluation of effects against planktonic cells Seviteronel were determined as the lowest concentration resulting in complete (100%) inhibition of growth (11). An XTT 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide-based colorimetric assay was applied for the evaluation of effects on biofilms (12). biofilms were prepared via a 96-well plate-based method (13). Briefly, conidia were collected from Sabouraud’s dextrose agar (SDA) and resuspended in 20 ml RPMI 1640. The suspension was then adjusted to the final concentration of 1 1 107 spores/ml. Subsequently, the suspension was added into the 96-well plate with 200 l in each cell and incubated at 37C for 72 h. The media were then carefully extracted without disturbing the biofilm. The 96-well plate was washed with sterile phosphate-buffered saline (PBS) three times to remove detached spores (13). Subsequently, the 96-well plate containing prepared biofilm was inoculated with 100 l serially double-diluted FK506 in the horizontal direction and another 100 l serially double-diluted azoles in the vertical Seviteronel direction. After incubation at 37C for 48 h, 50 l XTT-menadione solution was added to each well, achieving a working concentration of 1 1 g/ml, and then incubated for another 4 h. Subsequently, 80 l of the colored supernatant from each well was removed, transferred into a new plate, and read at 490 nm. The sessile MIC50 and MIC80 (SMIC50 and SMIC80) were defined as the concentrations at which a 50% or 80% decrease in optical density (OD) would be detected in comparison to the controls (12). The Seviteronel interactions between FK506 and azoles were classified on Seviteronel the basis of the fractional inhibitory concentration index (FICI). The FICI as calculated by the formula FICI = (Ac/Aa) + (Bc/Ba), where Ac and Bc are the MICs/SMICs of antifungal drugs in combination, and Aa and Ba are the MICs/SMICs of antifungal drugs A and B alone. The FICI results are classified as follows: FICI of 0.5, synergy; FICI of 0.5 to 4, no interaction (indifference); and FICI of 4, antagonism (14). All experiments were conducted in triplicate. The MIC ranges of individual tested agents against planktonic isolates were 16 g/ml for FK506, 0.5 to 1 1 g/ml for ITC, 0.25 to 0.5 g/ml for VRC, and 0.25 to 1 1 g/ml for POS (Table 1). FK506 individually did not show any significant antifungal activity against planktonic biofilms. No antagonism was observed in all combinations..