Detection of Gram-positive and Gram-negative bacteria membrane permeabilization induced by pulsed electric field using electrochemical admittance spectroscopy

Electrochemical impedance or admittance spectroscopy (EIS or EAS) has been widely used for decades, offering a label-free, rapid, real-time, and non-destructive assay for optically opaque and turbid bacterial solutions. However, PEF-induced changes in the bacterial envelope can present challenges in detecting the extent of membrane permeabilization in both Gram-positive and Gram-negative bacteria due to their distinct morphological properties. Here, we used a new approach for detecting bacterial membrane permeabilization induced by PEF using electrochemical admittance spectroscopy (EAS). The metabolic activity results have shown that the larger L. d. bulgaricus bacteria was found to be significantly more resistant to PEF strengths ranging from 4 to 16 kV/cm than the smaller E. coli bacteria at shorter PEF treatment durations (10 × 10 µs pulses). Interestingly, the difference in the increase of the admittance magnitude and a decrease in phase angle between the PEF treatment times of 10 × 10 µs and 10 × 100 µs pulses at different PEF strengths was more pronounced for E. coli bacteria samples. Our results demonstrate that EAS is more effective in comparing the degree of membrane permeabilization of Gram-positive and Gram-negative bacteria when longer PEF treatment durations are applied.