Cutibacterium acnes protects Candida albicans from micafungin effect 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 72h-old single-species biofilms of C. albicans and polymicrobial biofilms involving both C. albicans and C. acnes were formed in Brain Heart Infusion and observed by scanning electronic microscopy. 24h-old single-species and polymicrobial biofilms were treated for 24h by micafungin (concentrations ranging from 0.75 mg.L-1 to 12 mg.L-1 ) and anti-biofilm activity was evaluated on fungal cells by flow cytometry after addition of propidium iodide. Results showed that C. albicans and C. acnes formed a polymicrobial biofilm in tested conditions, and bacteria presence did not modify the fungal viability. Micafungin induced a fungal mortality rate ranging from 70% to 95% and from 35% to 40% in C. albicans single-species biofilms and C. acnes-C. albicans polymicrobial biofilms, respectively. Mortality induced by micafungin was significantly reduced (p<0.05 for micafungin at 6 mg.L-1 and p<0.001 for other concentrations) in polymicrobial conditions compared to single-species. In conclusion, this study showed that C. albicans and C. acnes are able to form polymicrobial biofilm together in a synergic way, and that this organization increases the yeast resistance to micafungin.