Nanosecond electric pulses rapidly enhance the inactivation of Gram-negative bacteria using Gram-positive antibiotics

Physically disrupting microorganism membranes to enable antibiotics to overcome resistance mechanisms that inhibit or excrete antibiotics has great potential for reducing antibiotic doses and rendering resistance mechanisms inert. We demonstrate the synergistic inactivation of a Gram-positive ( Staphylococcus aureus ) and two Gram-negative ( Escherichia coli and Pseudomonas aeruginosa ) bacteria by combining 222 30 kV/cm electric pulses (EPs) or 500 20 kV/cm EPs with 300-ns EP duration with various antibiotics with different mechanisms of action is demonstrated. Doses of antibiotics that produced no inactivation in 10 min of exposure in solution with bacteria induced several log reductions under the influence of nanosecond EPs. Combining 2 μg/L or 20 μg/mL of rifampicin with the 30 kV/cm EPs enhanced Staphylococcus aureus inactivation compared with EPs alone, while only a few of the other combinations demonstrated improvement. Combining 2 μg/L or 20 μg/mL of mupirocin or rifampicin with either EP train enhanced E. coli inactivation compared with EPs alone. Combining 2 μg/L or 20 μg/mL of erythromycin or vancomycin with the 30 kV/cm EPs enhanced E. coli inactivation compared with EPs alone. These results indicate that EPs can make Gram-positive antibiotics efficient for inactivating Gram-negative bacteria with future studies required to optimize EP parameters for other antibiotics and Gram-negative bacteria.