Membrane potential dynamics unveil the promise of Bioelectrical Antimicrobial Susceptibility Testing (BeAST) for anti-fungal screening

Membrane potential is a useful marker for antimicrobial susceptibility testing (AST) due to the fundamental characteristic of vital cells. However, the difficulties associated with measuring the membrane potential in microbes restrict its broad application. In this study, we present Bioelectrical AST (BeAST) using the model fungus Saccharomyces cerevisiae. Using fluorescent indicators (DiBAC4(3), ThT and TMRM), we measured plasma and mitochondrial membrane-potential dynamics upon electric stimulation. We find that a 2.5-second electric stimulation induces hyperpolarisation of plasma membrane lasting 20 minutes in vital S. cerevisiae, but depolarisation in inhibited cells. The numerical simulation of FitzHugh-Nagumo model successfully recapitulates vitality-dependent dynamics. The model also suggests that the magnitude of plasma-membrane potential dynamics (PMD) correlates with the degree of inhibition. To test this prediction and to examine if BeAST can be used for assessing novel anti-fungal compounds, we treat cells with biogenic silver nanoparticles (bioAgNPs) synthesised using orange fruit flavonoids and Fusarium oxysporum. Comparing BeAST with optical density assay with various stressors, we show that PMD correlates with the severityof growth inhibitions. These results suggest that BeAST holds promise for screening anti-fungal compounds, offering a valuable approach to tackling antimicrobial resistance.