Background: Candida biofilms are difficult to treat due to reduced susceptibility in biofilm. We investigate the activity of rifampin (RIFA) alone and in combination with amphotericin B (AMPB) against planktonic and biofilm Candida by measuring growth-related heat production using a novel real-time and highly sensitive assay (microcalorimetry).
Material/methods: C. albicans (ATCC 90028), C. glabrata (DSY 562) and C. parapsilosis (ATCC 22019) were tested. Microcalorimetry was performed using an isothermal calorimeter (TAM III, TA Instruments) at 37°C in sealed glass ampoules containing RPMI medium. Planktonic Candida (1-5x105 CFU) were added to RPMI containing serial dilution of RIFA alone or in combination with AMPB. Candida biofilm was formed on porous glass beads and calorimetry was used in order to quantify the recovering yeasts. The minimal heat inhibitory concentration (MHIC) was defined as the lowest antifungal concentration reducing the heat-flow peak by 50% for RIFA and by 90% for AMPB at 24 h for planktonic and at 48 h for biofilm growth. Synergism was defined as delay in heat production >4 h or MHIC reduction of ≥2x.
Results: Table 1 shows the MHIC of RIFA and AMPB against planktonic and biofilm Candida. RIFA showed no heat inhibition, whereas AMPB inhibited Candida at 0.125-0.25 µg/ml in planktonic and at 1-8 µg/ml in biofilm growth. When combined, RIFA reduced the MHIC of AMPB by 8x, 4x and 2x against planktonic C. albicans, C. glabrata and C. parapsilosis, respectively, and by 4x and 8x against biofilm C. glabrata and C. parapsilosis, respectively (Figure 1).
Conclusions: Addition of RIFA to AMPB increased the activity against planktonic and biofilm Candida spp. Further combinations need to be tested in order to evaluate the potential synergistic effect between RIFA and antifungals.
Full conference title:
- ECCMID 26th (2016)