Micafungin is more active against Candida albicans biofilms with high metabolic activity.

BACKGROUND: The ability to form biofilm enables Candida spp. to cause catheter-related candidaemia. The use of agents with in vitro activity against Candida albicans biofilms, such as micafungin, could obviate catheter removal. The metabolic activity of C. albicans biofilms is strain-dependent, and cell wall formation is thought to be more prominent in biofilms showing high metabolic activity.

METHODS: We studied the antifungal activity of micafungin against 265 C. albicans isolates with different degrees of metabolic activity causing fungaemia in 246 patients admitted to Gregorio Marañón Hospital (January 2007 to June 2013). All strains were classified according to the metabolic activity of their biofilm, which was classified as low, moderate and high using XTT. Micafungin MICs for planktonic and sessile cells were assessed using the EUCAST E.Def 7.2 procedure and XTT reduction assay, respectively. The MIC was defined as a 50% and 80% reduction in metabolic activity compared with the control well.

RESULTS: Micafungin was uniformly more active against planktonic cells than against sessile cells (MIC50 ≤ 0.015 versus 8 mg/L), although it was not consistently active against all C. albicans biofilms. Isolates with low metabolic activity biofilms showed the lowest susceptibility to micafungin, followed by moderate and high metabolic activity biofilms (P < 0.001).

CONCLUSIONS: Our study suggests that the metabolic activity of biofilm may have a role in future evaluations of micafungin for the eradication of C. albicans biofilms (e.g. the lock therapy approach).