The Influence of Moderate Electroporation on E. coli Membrane Permeability

This study examined the membrane permeability of E. coli, which were exposed to a moderate pulsed electric field (PEF) (3.3 kV/cm). The membrane permeability of E. coli was examined as a function of time after exposure to PEF. When comparing the percentage of propidium iodide (PI) permeability at a given time from PEF exposure, it appeared that as the bacterial density increased, there was a decrease in PI permeability. The permeability to PI in the bacterial suspensions of 0.05, 0.1, and 0.5 OD, 90 min after exposure, was 56.4 ± 4.08%, 43.91 ± 0.75%, and 29.47 ± 3.31%, respectively. Membrane permeability was also examined in different phosphate-buffered saline (PBS) concentrations. At 0.05 OD there was a linear correlation between PBS concentrations (0.56, 0.75, and 1 mM) and PI permeability (28.36 ± 2.22%, 61.08 ± 3.17%, and 98.2 ± 0.9%, respectively). At the higher bacterial densities of 0.1 and 0.5 OD, this phenomenon was not evident. Examination of bacterial membrane permeability using 4, 70, and 250 kDa fluorescein isothiocyanate (FITC)-dextran revealed that PEF led to 4kDa FITC-dextran permeabilization of 27.94 ± 3.76%. The PEF parameters used did not influence the bacterial cell size and viability. This study shed light on bacterial membrane permeability as a function of conductivity and bacterial density under PEF exposure.