# Fast detection of synergy and antagonism in antifungal combinations used against Candida albicans clinical isolates

## TL;DR

This paper introduces a fast and cost-effective method to test antifungal drug interactions in Candida albicans, revealing isolate-specific synergy patterns.

## Contribution

A novel in vitro method for rapid assessment of antifungal synergy and antagonism in C. albicans clinical isolates.

## Key findings

- Amphotericin B and fluconazole showed synergy in 1% of isolates.
- Anidulafungin and fluconazole showed synergy in 19.5% of isolates.
- Amphotericin B and anidulafungin showed synergy in 23.9% of isolates.

## Abstract

The rise in antifungal resistance has limited treatment options for serious fungal infections, emphasizing the need for effective combination therapies. However, low-cost and rapid systems to evaluate synergy and antagonism in antifungal combinations are lacking. Here, we introduce a novel in vitro testing method for assessing antifungal interactions in C. albicans, enabling the simultaneous testing of three antifungal agents in a single agar plate with overnight results. This method, validated against the checkerboard assay, provides consistent fractional inhibitory concentration (FICi) measurements with reduced variability and workload. We applied this method in a comprehensive screen of 92 clinical C. albicans isolates for three antifungals—amphotericin B, fluconazole, and anidulafungin—yielding assessments of a total of 276 distinct combinations of antifungals and isolates. Results revealed isolate-specific interaction patterns, with amphotericin B and fluconazole showing synergy in 1% of isolates, anidulafungin and fluconazole in 19.5%, and amphotericin B and anidulafungin in 23.9%. These findings underscore the need for isolate-specific testing in clinical settings. This proposed assay aims to present a solution to that as a scalable high throughput approach to this clinical problem.

The online version contains supplementary material available at 10.1038/s41598-025-22870-x.