Membrane Potential Assay

To examine the perturbation of the cell membrane of S. aureus by IBG, the membrane potential of the cells was measured by fluorescence spectrometry using fluorescent probe DiOC₂(3), as described previously (Wang et al., 2017). Bacterial cells were energized by the addition of glucose to establish a proton motive force (negative and basic inside the cell). This led to an increase in fluorescence associated with aggregation of the DiOC₂(3). Upon addition of the ionophore CCCP, the Δψ was dissipated and the fluorescence intensity dropped to the level before addition of glucose. All assays were performed at least twice.