Influence of azoles on mixed long-term continuous flow cultures of Candida albicans and Candida glabrata under aerobic and anaerobic conditions

H. Bernhardt, M. Knoke, K. Zimmermann, G. Schwesinger, J. Bufler, K. Ludwig, J. Bernhardt

Author address: 

Greifswald, Karlsruhe, Rostock, DE

Abstract: 

Objectives: Around 3% of cultures obtained from candidaemia patients and 13% of those from oesophageal candidiasis patients grew both C. albicans and C. glabrata. A continuous flow system was used to investigate the effects of fluconazole (FLU) and voriconazole (VORI) on mixed Candida infections under aerobic and anaerobic conditions. This allows the simulation of the in vivo situation. Methods: Candida strains were cultured at 37°C in double-wall vessels containing 110 ml medium. Anaerobic conditions were obtained by flushing with N2/CO2; aerobic conditions were maintained with pressurized air. Media flow rate was 6.0 ml/h. The system was adjusted to a generation time of 15-20 h. Media contained FLU (20 or 60 mg/l), VORI (20 mg/l) or no antifungal (controls). For the detection of morphologic alterations of the Candida cells half-size slides were kept in the culture vessels. At the end of the trials the biofilms on the slides were stained with BLANKOPHOR® (Bayer AG Leverkusen, Germany) and examined by fluorescence microscopy. Results: Growth of C. glabrata was particularly strong in co-culture with C. albicans. C. glabrata consistently achieved higher densities than C. albicans (7.5 vs. 6.6 log10 cfu/ml). In this setting, C. albicans was inhibited more effectively than C. glabrata by 20 and 60 mg/l FLU. At 60 mg/l, FLU inhibited C. glabrata more effectively under anaerobic conditions and after 96 h. Clinical isolates and type strains of both C. albicans and C. glabrata were inhibited more strongly by FLU and VORI under anaerobic conditions. The decrease in germ counts after addition of FLU or VORI to a C. albicans monoculture was more rapid and more profound under anaerobic (>99%; i.e. fungicidal) than aerobic conditions (90-99%; i.e. fungistatic). Both FLU and VORI strongly inhibited biofilm formation: in the absence of antifungals, a biofilm of budding yeast, mycelia and pseudomycelia developed on glass slides. In the presence of FLU or VORI, only few yeast cells and germ tubes were observed, but no mycelia or pseudomycelia. Conclusion: In a long-term continuous flow culture system, the inhibition of various Candida strains by FLU or VORI was strongly enhanced by anaerobic conditions. This finding may be of relevance for the clinical setting, as mycotic abscesses and sequestered areas of infected tissue are hypoxic.
2006

abstract No: 

P1231

Full conference title: 

16th European Congress of Clinical Microbiology and Infectious Diseases
    • ECCMID 16th (2006)