Time-kill assays of amphotericin B plus anidulafungin against Candida tropicalis biofilms formed on two different biomaterials

Abstract

Purpose:

To determine the fungicidal activity by time-killing assays of amphotericin B (AMB) combined with anidulafungin (ANF) against biofilms of 2 clinical isolates of Candida tropicalis and the reference strain ATCC® 750, developed on polytetrafluoroethylene (PTFE) and titanium, using the CDC Biofilm Reactor (CBR) as an in vitro model.

Methods:

Biofilms were developed for 24 hours on the disk surfaces and then exposed to AMB (40 mg/L), ANF (8 mg/L), alone and combined. At predetermined time points after drug exposure, biofilms were removed from the disk surface by vortexing-sonication to quantify viable biofilm cells.

Results:

Drug activity was dependent on strain and time. After exposure to AMB, the mean decrease in viable cells attached to PTFE was 2.23 ± 0.89 Log₁₀ cfu/cm² (range 0.6-3.56 Log₁₀), and on titanium 2.91 ± 1.04 (range 1.49-4.51 Log₁₀). The reduction with ANF was 0.78 ± 0.5 (0.03-1.58 Log₁₀) on PTFE and 0.8 ± 2.26 (0.42-1.16 Log₁₀) on titanium. The reduction obtained with the combination of AMB + ANF was 1.8 ± 1.07 (0.22-3.54 Log₁₀) on PTFE and 1.97 ± 0.49 (1.36-2.84 Log₁₀) on titanium. The interaction was classified as indifferent with a tendency to antagonism.

Conclusions:

The activity of antifungal agents depends on the biomaterial surfaces the biofilm forming capacity of the isolate. AMB + ANF is less effective than AMB alone on both surfaces. Thus, the combination of these antifungals does not seem to add additional benefits to the treatment of C. tropicalis biofilm-related infections.