MORPHOLOGICAL-CHANGES OF SALMONELLA-TYPHIMURIUM CAUSED BY ELECTRICAL-STIMULATION IN VARIOUS SALT-SOLUTIONS

To better understand what physical changes occur in bacteria subjected to low-voltage, low-current electrical stimulation (ES), morphologica l changes in Salmonella typhimurium killed by ES were examined using e lectron microscopy. Cells (10(7) CFU/ml) were suspended in 0.015 M NaC l, 0.015 M Na2CO3, or 0.005 M Na3PO4 . 12H(2)O solutions and pulsed el ectric signals at 10 mA/cm(2) current, 1 kHz frequency and 50% duty cy cle were applied until more than 90% of the cells were dead. In NaCl s olutions, 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 Na3PO4 solutions, t he cytoplasm was scattered into small aggregates within the cell and m any fibrils were formed outside. The results of this research suggest that the mechanisms of destruction of S. typhimurium by ES depend on t he salt used as an electrolyte.