Susceptibility of Candida albicans biofilms to azithromycin, tigecycline and vancomycin and the interaction between tigecycline and antifungals

Despite growing data on antimicrobial lock therapy (ALT) in treating bacterial catheter-related bloodstream infections (CR-BSIs), ALT has not been established as a treatment option for CR-BSI caused by Candida albicans. Based on our finding that high-dose doxycycline exhibited antifungal activity against mature C. albicans biofilms, we evaluated additional antibacterial agents with Gram-positive activity [azithromycin, tigecycline (TIG) and vancomycin]. After screening these antibiotics, it was found that TIG had substantial antifungal activity against mature C. albicans biofilms. Therefore, TIG was assayed alone and in combination with fluconazole (FLC), amphotericin B (AmB) or caspofungin (CAS). TIG at 2048 mu g/mL resulted in a >50% reduction in the growth of planktonic C. albicans cells. TIG inhibited the formation of biofilms from 128 mu g/mL. Against mature biofilms, 2048 mu g/mL TIG reduced metabolic activity by 84.2%. Furthermore, addition of 512 mu g/mL TIG to FLC at all concentrations tested provided additional reduction in the metabolic activity of mature biofilms. However, this was not superior to 512 mu g/mL TIG alone. TIG at 512 mu g/mL increased the antifungal effect of lower concentrations of AmB (0.03125-0.25 mu g/mL), but at 0.03125 mu g/mL and 0.0625 mu g/mL this effect was not superior to 512 mu g/mL TIG alone. TIG inhibited the antifungal effect of higher concentrations of AmB (>= 2 mu g/mL). TIG at 512 mu g/mL inhibited the antifungal activity of CAS at lower concentrations (0.25-8 mu g/mL). These data indicate that high-dose TIG is highly active in vitro against planktonic cells, forming biofilms and mature biofilms of C. albicans. Published by Elsevier B.V. on behalf of International Society of Chemotherapy.