Mediated electrochemical method for the analysis of membrane damage effects of phenolic compounds to Staphylococcus aureus

• Single ferricyanide mediator was used as a probe for membrane damage assay.
• Microelectrode voltammogram was used for ferrocyanide measurement.
• AFM, potassium efflux and respiration inhibition were also used for comparison purpose.

In this study, the mediated electrochemical method and conventional methods, including the atomic force microscopy, respiration inhibition, and potassium efflux methods were integrated for the analysis of the membrane damage effects of phenolic compounds to the food contamination bacteria Staphylococcus aureus (S. aureus). Hydrophilic ferricyanide, acting as both the permeability indicator and intracellular redox activity indicator, was employed as the mediator. Microelectrode voltammetric method was used to assay the ferrocyanide accumulations arising from the reduction of ferricyanide by the NADH: Fe3 + reductase embedded in the cell membrane. When the samples with S. aureus suspensions were incubated for 2 h, the mediated electrochemical response increased by 71.9% due to the presence of 3 mM carvacrol, which was consistent with the significant potassium efflux attributed to the presence of the carvacrol, indicating the outer membrane damage of the bacteria. However, the relative respiration activities of the S. aureus suspensions remained 32.5% of the controlled sample, which suggested the damage of the respiration chain due to the presence of 3 mM carvacrol. The mediated electrochemical method was also applicable to the other three phenolic compounds including eugenol, thymol, and 3-isopropylphenol, exhibiting the applicability of the mediated electrochemical method for the membrane damage effect of the phenolic compounds to bacteria.