The Inhibitory Effect of Human Beta-defensin-3 on Candida Glabrata Isolated from Patients with Candidiasis

ABSTRACT

Candida glabrata is a common non-albicans Candida species found in patients with candidiasis and it sometimes develops antifungal resistance. Human beta-defensin-3 (hBD-3) is an antimicrobial peptide of immune system active against various types of microbes including Candida spp. This study investigated antifungal activity of hBD-3 and its synergistic effect with a first-line antifungal agent on C. glabrata clinical isolates. Candida spp. were characterised in patients with candidiasis. The antifungal activities of hBD-3 and fluconazole against C. glabrata were evaluated using Broth microdilution assay. The synergistic activity of these two agents was determined by checkerboard microdilution and time-killing assays. The cytotoxicity of hBD-3 was evaluated using LDH-cytotoxicity colorimetric assay. Of 307 episodes from 254 patients diagnosed with candidiasis, C. glabrata was found in 21 clinical isolates. Antifungal susceptibility tests of C. glabrata were performed, fluconazole demonstrated an inhibitory effect at concentrations of 0.25-8 μg/ml, but one antifungal resistant strain was identified (>64 μg/ml). hBD-3 showed an inhibitory effect against all selected strains at concentrations of 50-75 μg/ml and exhibited a synergistic effect with fluconazole at the fractional inhibitory concentration index (FICI) of 0.25-0.50. A concentration of 25 μg/ml of hBD-3 alone showed no cytotoxicity but synergistic activity was seen with fluconazole. In conclusion, hBD-3 has antifungal activity against C. glabrata and synergistic effects with fluconazole at concentrations that alone, have no cytotoxicity. hBD-3 could be used as an adjunctive therapy with first-line antifungal agents for patients with C. glabrata infection particularly those infected with fluconazole-resistant strains.

KEYWORDS:

• Human beta-defensin
• candida glabrata
• candidiasis

Acknowledgments

We would like to thank Translational Research in Inflammation and Immunology Research Unit, Immunology Unit and Mycology Unit, Department of Microbiology, Faculty of Medicine, and Medical Microbiology, Interdisciplinary Program, Graduate School, Chulalongkorn University, and Institute of Dermatology, Bangkok, Thailand.

Special thanks go to the Development and Promotion of Science and Technology Talents Project (DPST), Rachadapisek Sompod Endowment Foundation (No. RA62/006), and the Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand for financial support.

Authorship contributions

TI performed the experiments; TI, AT, SV, CK, and SWE co-wrote the manuscript; DC designed the study and co-wrote the manuscript.

Additional information

Funding

This work was supported by the Ratchadapisek Sompoch Endowment Fund [No. RA62/006].