TEM/EDX analysis of bacterial spores treated by nanosecond pulsed electric fields

This paper describes killing bacterial spores using highly energized pulsed electric fields under pressurized conditions. B. subtilis spores suspended in a conductive liquid were repetitively subjected to 100 kV/cm, 100 ns pulsed electric fields. The PEF treatment lowers the sterilization temperature by 10°C and the spore number was reduced by the logarithmic number of 6.7. Also the killing mechanism was discussed on the basis of element analysis using a transmission electron microscopy (TEM) equipped with an energy dispersive X-ray spectrometer (EDX). In the heat treatment (121°C, 14 s), the core contents including phosphorus leak into cortex which indicates the damage of the inner membrane, whereas the coat structure still remains. Both the core membrane and the coat were damaged in the PEF treatment.