Morphological changes of salmonella typhimurium caused by electrical Stimulation in various salt solutions

Abstract

To better understand what physical changes occur in bacteria subjected to low-voltage, low-current electrical stimulation (ES), morphological changes in Salmonella typhimurium killed by ES were examined using electron microscopy. Cells (107 CFU/ml) were suspended in 0.015 M NaCl, 0.015 M Na 2CO3, or 0.005 M Na3PO4· H2O solutions and pulsed electric signals at 10 mA/cm2 current, 1 kHz frequency and 50% duty cycle were applied until more than 90% of the cells were dead. In NaCl solutions, cells were swollen before collapsing into amorphous bodies. In Na2CO3 solutions, cells showed irregular surfaces and the cytoplasm became less dense at the centers of the cells. In Na2PO4 solutions, the cytoplasm was scattered into small aggregates within the cell and many fibrils were formed outside. The results of this research suggest that the mechanisms of destruction of S. typhimurium by ES depend on the salt used as an electrolyte. Copyright ©, International Association of Milk, Food and Environmental Sanitarians.