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Combined Antifungal Activity of Fluconazole and Berberine Against a Fluconazole-Resistant Clinical Isolate of Candida albicans: An In Vitro Agar Well Diffusion Study

Rasool Chaloob Hulyal1, Dawood Chaloob Hulyal2
1Department of Pharmacology and Toxicology, College of Pharmacy, University of Basrah, Basrah, Iraq
2Department of Clinical Laboratory Sciences, College of Pharmacy, University of Basrah, Basrah, Iraq
DOI: https://doi.org/10.70517/revcc2624143
Published: 08/10/2026
: Rasool Chaloob Hulyal, Dawood Chaloob Hulyal. Combined Antifungal Activity of Fluconazole and Berberine Against a Fluconazole-Resistant Clinical Isolate of Candida albicans: An In Vitro Agar Well Diffusion Study. Revista Cultura Científica, 2026 Issue 24. pg. 1733-1743.

Abstract

Oral candidiasis caused by Candida albicans is a common opportunistic fungal infection, and reduced susceptibility or resistance to fluconazole can complicate treatment in repeatedly exposed or otherwise high-risk patients. Berberine, an isoquinoline alkaloid found in Berberis, Coptis, and related plants, has previously been reported to enhance fluconazole activity against resistant Candida isolates. This in vitro experimental study screened fluconazole and berberine, alone and in combination, against a fluconazole-resistant clinical isolate of C. albicans. A collection of 40 fluconazole-resistant C. albicans isolates had been obtained from 50 clinical specimens and identified by conventional mycological methods together with chromogenic media and the Vitek 2 system; the combination experiment reported in this article was performed on one resistant clinical isolate. Resistance status was established by antifungal susceptibility testing, while the quantitative outcome reported here was inhibition-zone diameter in an agar well diffusion assay. Each reported diffusion condition was tested in triplicate. Fluconazole produced a detectable zone only at 25 μg per well, with a mean diameter of 13.00 ± 0.00 mm. Berberine alone produced no detectable zone at any tested amount. The nominal combination of fluconazole 25 μg with berberine 250 μg produced a zone of 32.50 ± 2.50 mm, corresponding to a mean difference of 19.50 mm compared with fluconazole alone (95% CI 13.29–25.71 mm by the Welch approach). The three highest-dose comparison groups differed overall (one-way ANOVA, F(2,6) = 385.32, p < 0.0001; Kruskal–Wallis H = 7.71, p = 0.021), and the combination differed from fluconazole alone (Welch t = 13.51, df = 2.0, p = 0.0054; pooled-variance Student t = 13.51, df = 4, p = 0.00017). Because berberine alone produced no measurable inhibition zone, the larger zone observed with the combination is consistent with potentiation of fluconazole activity. However, agar well diffusion cannot formally establish pharmacodynamic synergy, and confirmation by checkerboard broth microdilution with a fractional inhibitory concentration index and by time–kill analysis is required.

Keywords: Candida albicans, fluconazole, berberine, antifungal resistance, drug combination, agar well diffusion

Abstract

Oral candidiasis caused by Candida albicans is a common opportunistic fungal infection, and reduced susceptibility or resistance to fluconazole can complicate treatment in repeatedly exposed or otherwise high-risk patients. Berberine, an isoquinoline alkaloid found in Berberis, Coptis, and related plants, has previously been reported to enhance fluconazole activity against resistant Candida isolates. This in vitro experimental study screened fluconazole and berberine, alone and in combination, against a fluconazole-resistant clinical isolate of C. albicans. A collection of 40 fluconazole-resistant C. albicans isolates had been obtained from 50 clinical specimens and identified by conventional mycological methods together with chromogenic media and the Vitek 2 system; the combination experiment reported in this article was performed on one resistant clinical isolate. Resistance status was established by antifungal susceptibility testing, while the quantitative outcome reported here was inhibition-zone diameter in an agar well diffusion assay. Each reported diffusion condition was tested in triplicate. Fluconazole produced a detectable zone only at 25 μg per well, with a mean diameter of 13.00 ± 0.00 mm. Berberine alone produced no detectable zone at any tested amount. The nominal combination of fluconazole 25 μg with berberine 250 μg produced a zone of 32.50 ± 2.50 mm, corresponding to a mean difference of 19.50 mm compared with fluconazole alone (95% CI 13.29–25.71 mm by the Welch approach). The three highest-dose comparison groups differed overall (one-way ANOVA, F(2,6) = 385.32, p < 0.0001; Kruskal–Wallis H = 7.71, p = 0.021), and the combination differed from fluconazole alone (Welch t = 13.51, df = 2.0, p = 0.0054; pooled-variance Student t = 13.51, df = 4, p = 0.00017). Because berberine alone produced no measurable inhibition zone, the larger zone observed with the combination is consistent with potentiation of fluconazole activity. However, agar well diffusion cannot formally establish pharmacodynamic synergy, and confirmation by checkerboard broth microdilution with a fractional inhibitory concentration index and by time–kill analysis is required.

Keywords: Candida albicans, fluconazole, berberine, antifungal resistance, drug combination, agar well diffusion

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Rasool Chaloob Hulyal
Department of Pharmacology and Toxicology, College of Pharmacy, University of Basrah, Basrah, Iraq
rasool.hulyal@uobasrah.edu.iq
Dawood Chaloob Hulyal
Department of Clinical Laboratory Sciences, College of Pharmacy, University of Basrah, Basrah, Iraq

How to cite:

Rasool Chaloob Hulyal, Dawood Chaloob Hulyal. Combined Antifungal Activity of Fluconazole and Berberine Against a Fluconazole-Resistant Clinical Isolate of Candida albicans: An In Vitro Agar Well Diffusion Study. Revista Cultura Científica, 2026 Issue 24. pg. 1733-1743.

Publication History

  • Received: 30/07/2026
  • Accepted: 01/10/2026
  • Published: 08/10/2026
Copyright © 2026, Rasool Chaloob Hulyal, Dawood Chaloob Hulyal. Published by Revista Cultura Científica. This article is published as open access under the Creative Commons Attribution 4.0 International (CC BY 4.0) license (http://creativecommons.org/licenses/by/4.0/).

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