Alteration of Zeta potential and membrane permeability in bacteria: a study with cationic agents

Abstract

In the present study, we have tried to establish the correlation between changes in Zeta potential with that of cell surface permeability using bacteria (Escherichia coli and Staphylococcus aureus). An effort has been made to establish Zeta potential as a possible marker for the assessment of membrane damage, with a scope for predicting alteration of cell viability. Cationic agents like, cetyl trimethyl ammonium bromide and polymyxin B were used for inducing alteration of Zeta potential, and the changes occurring in the membrane permeability were studied. In addition, assessment of poly-dispersity index (PDI), cell viability along with confocal microscopic analysis were performed. Based on our results, it can be suggested that alteration of Zeta potential may be correlated to the enhancement of membrane permeability and PDI, and it was observed that beyond a critical point, it leads to cell death (both Gram-positive and Gram-negative bacteria). The present findings can not only be used for studying membrane active molecules but also for understanding the surface potential versus permeability relationship.

Keywords: Cell viability; Membrane permeability; Polydispersity index (PDI); Zeta potential.

Fig. 1

Change in bacterial (a, c E. coli: b, d S. aureus) Zeta potential and membrane permeability (assayed by NPN uptake) in presence of different concentrations of CTAB (a, b) and polymyxin B (c, d). Percentage change in Zeta potential (solid lines) and percentage change in permeability (dashed lines) was plotted against the concentration (µg/ml) of the treatment

Fig. 2

Change in bacterial (a, b E. coli; c, d S. aureus) membrane permeability (assayed by crystal violet uptake) in presence of different concentrations of CTAB (a, c) and polymyxin B (b, d). Percentage of crystal violet uptake was plotted against the concentration (µg/ml) of the treatment

Fig. 3

E. coli (a, b) and S. aureus (c, d) cells were treated with different concentrations of CTAB (a, c) and ampicillin (b, d). Viability of the cells is the common parameter which has changed in a dose dependent manner for both of the agents, thus percentage change in Zeta potential (ZP; dashed red line) and percentage change in permeability (solid black line) was plotted against percentage of viable cells

Fig. 4

Bacterial cell suspension (CTAB 30 µg/ml and untreated Blank) stained with Syto-9 and PI analysed by CLSM. Cells with intact cell surface (membrane undisturbed) stained fluorescent green, whereas cells with ruptured surface (altered membrane integrity) stained fluorescent red. The overlap of the red and greens appear as orange