Efficacy of anidulafungin against biofilms of different Candida species in long-term trials of continuous flow cultivation

Long-term continuous flow culture allows the investigation of dynamic biofilms under microaerophilic or aerobic conditions. We studied the biofilm formation and changes of susceptibility in 30 blood culture isolates (48 experiments) of different Candida species exposed to anidulafungin in 0.16 ml or 7.7 ml flow chambers. The flow rate (F) was adjusted to a very low rate of 1.3 ml h(-1) resulting in an exchange rate of up to 180 and 6.25 times chamber volumes per 24 hours in the small and large chambers, respectively. The results of culture at a very low flow rate were markedly different from cultures in micro well plates. Low flow rates may better mimic the in vivo situation and thus may be of higher relevance for the clinical setting. Under these conditions, a general resistance of fungal biofilms against anidulafungin cannot be confirmed. Strains of C. albicans and C. glabrata showed very uniform results whereas the C. parapsilosis group and C. lusitaniae varied from high susceptibility to resistance. Species differentiation of the C. parapsilosis group appears to be appropriate in clinical microbiological diagnostics. For the majority of the tested Candida species, anidualafungin was more effective than voriconazole. For the species C. lusitaniae and C. guilliermondii susceptibility testing should be considered prior to clinical use of echinocandin antifungals.