Cutibacterium acnes protects Candida albicans from the effect of micafungin in biofilms

The aim of this study was to investigate the ability of Candida albicans and Cutibacterium acnes to grow together as a polymicrobial biofilm in vitro and to examine the influence of C. acnes on C. albicans susceptibility to micafungin. Mature 72-h-old single-species biofilms of C. albicans and polymicrobial biofilms involving both C. albicans and C. acnes were formed in brain-heart infusion and were observed by scanning electronic microscopy. Moreover, 24-h-old single-species and polymicrobial biofilms were treated for 24 h with micafungin (concentrations ranging from 0.75 mg/L to 12 mg/L) and the antibiofilm activity of micafungin was evaluated on fungal cells by flow cytometry following addition of propidium iodide. The results showed that C. albicans and C. acnes formed a polymicrobial biofilm in the tested conditions and that bacterial presence did not modify fungal viability. Micafungin induced a fungal mortality rate ranging from 70-95% in C. albicans single-species biofilms and from 35-40% in C. acnes-C. albicans polymicrobial biofilms. Mortality induced by micafungin was significantly reduced (P < 0.05 for micafungin at 6 mg/L and P < 0.001 for other micafungin concentrations) in polymicrobial conditions compared with single-species biofilms. In conclusion, this study showed that C. albicans and C. acnes are able to form polymicrobial biofilms together in a synergistic way and that this organisation increases yeast resistance to micafungin.