Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Biophysics

Effect of extremely low frequency positive electric pulse with different duty cycles on pseudomonas aeruginosa (ATCC: 27853) growth by constructed and implemented exposure device was investigated in this study. The exposure device was applied to give extremely low frequency in the range of 0.1 Hz up to 20 Hz. Additional option in the exposure device was to control the duty cycle of the pulse with variation from 10% up to 100%. Growth curves of pseudomonas aeruginosa were investigated before and after exposure to different frequencies (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 Hz) through measuring the optical density and cell count for confirmation of data. Exposures to resonance frequency in the whole ranges of duty cycles provided by the designed device were done. These studies were followed by DNA fragmentation technique, transmission electron microscope (TEM), antibiotic susceptibility tests, and dielectric measurements for exposed and unexposed microorganism. Results revealed inhibition effect by 48.56 % and 47.4% together with change in the DNA structural properties for samples exposed to 0.5 Hz and 0.7 Hz respectively. Moreover the data indicated important role of duty cycle on the inhibition mechanism. Furthermore, two different mechanisms of interaction between positive electric pulse and microorganism occurred; 0.5 Hz caused rupture in cell wall while 0.7 Hz caused denaturation of the inner consistent of the cell.

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