Listeria monocytogenes cell wall constituents exert a charge effect on electroporation threshold

Genetically engineered cells with mutations of relevance to electroporation, cell membrane permeabilization by electric pulses, can become a promising new tool for fundamental research on this important biotechnology. Listeria monocytogenes mutants lacking DltA or MprF and assayed for sensitivity to the cathelicidin like anti-microbial cationic peptide (mCRAMP), were developed to study the effect of cell wall charge on electroporation. Working in the irreversible electroporation regime (IRE), we found that application of a sequence of 50 pulses, each 50μs duration, 12.5kV/cm field, delivered at 2Hz led to 2.67±0.29 log reduction in wild-type L. monocytogenes, log 2.60±0.19 in the MprF-minus mutant, and log 1.33±0.13 in the DltA-minus mutant. The experimental observation that the DltA-minus mutant was highly susceptible to cationic mCRAMP and resistant to IRE suggests that the charge on the bacterial cell wall affects electroporation and shows that this approach may be promising for fundamental studies on electroporation.